'Thank you very much, sir,' said Biggles respectfully, but inwardly he was thinking, 'Yes, I'll bet you will, you old liar,' knowing the man's reputation for taking all the credit he could get regardless of whom it really concerned. He was tempted to ask about the machine that had just taken off, but decided on second thoughts that perhaps it would be better not to appear inquisitive.

'Yes, I must be getting along,' repeated the Count, rising. 'By the way, I'll have one of your cigarettes.' He reached for the box.

'Try one of these, sir: they're better,' invited Biggles, whipping out his case and opening it. To his infinite relief the Count selected one, lit it, and moved towards the door.

'See you at dinner,' he said with a parting wave.

Biggles bowed and saluted in the true German fashion as his Chief departed, but as the door closed behind him he sat down limply and wiped the perspiration from his forehead. 'These shocks will be the death of me if nothing else is,' he muttered weakly, and glanced at his watch. He sprang to his feet and moved swiftly, as he saw that he had exactly one hour and ten minutes to complete his task and get back to the Mess before the gong sounded for dinner, when he would have to be present or his absence would be remarked upon.

He picked up the box, opened it, took out the metal cylinder it contained and examined it with interest. Down one side was a graduated gauge, marked in minutes, and operated by a small, milled screw. On the top was a small red plunger which carried a warning to the effect that the bomb would commence to operate from the moment it was depressed.

Not without some nervousness he screwed the gauge to its limit, which was thirty minutes, replaced the bomb in its box, and slipped it into his pocket. Then, picking up his cap and leaving the light still burning, he set off on his desperate mission.

The distance to the hill on which the reservoir was situated was not more than half a mile in a straight line, but he deliberately made a detour in order to avoid meeting any soldiers of the camp who might be returning from the village. He had become so accustomed to unexpected difficulties and dangers that he was both relieved and surprised when he reached the foot of the hill without any unforeseen occurrence; he found a narrow track that wound upwards towards the summit, and followed it with confidence until he reached the reservoir.

It was an elevated structure built up of several thicknesses of granite blocks to a height of perhaps five feet above the actual hill-top, and seemed to be about three-quarters full of water, a fact that he ascertained by the simple expedient of looking over the wall.

Searching along the base, he found a place where the outside granite blocks were roughly put together, leaving a cavity wide enough to admit the bomb. The moon was just showing above the horizon, but a cloud was rapidly approaching it, so without any more ado he took the bomb from its case, forced the plunger home, and thrust it into the side of the reservoir. For a moment he hesitated, wondering as to the best means of disposing of the box; finally, he pushed it in behind the bomb, where its destruction would be a.s.sured. Then he set off down the hill just as the cloud drifted over the face of the moon.

He had taken perhaps a dozen paces when he was pulled up short by what seemed to be a barbed-wire fence; at first he could not make out what it was, but on looking closer he could just make out a stoutly built wire entanglement. An icy hand seemed to clutch his heart as he realized that it was unscalable, and that he was trapped within a few yards of a bomb which might, if there was any fault in its construction, explode at any moment.

Anxiously he looked to right and left, hoping to see the gap through which the path had led, but in the dim light and on the rocky hill-side he perceived with a shock that, having lost it, it might be difficult to find again.

The next five minutes were the longest he could ever remember. Stumbling along, he found the gap at last, as he was bound to by following the fence, but his nerves were badly shaken, and he ran down the path in a kind of horrible nightmare of fear that the bomb would explode before he reached camp.

'No more of this for me,' he panted, as, tripping over cactus and camel-thorn in his haste, he made his way by a roundabout course to the aerodrome. He struck it at the end of the tarmac, and was hurrying towards his quarters when he heard a sound that made him look upwards in amazement. It was the wind singing in the wires of a gliding aeroplane that was coming in to land.

It taxied in just as he reached the point where he had to turn to reach his room, and in spite of his haste, with the memory of the Arab still fresh in his mind, he paused to see who was flying in such strange conditions. He was half disappointed therefore when he saw Mayer climb out of the front seat of the machine, a Halberstadt, and stroll round to the tail unit to examine the rudder as if it was not working properly. There appeared to be no pa.s.senger, so without further loss of time Biggles went to his room, washed, brushed his clothes, and then went along to the dining-room. As he entered his eyes went instinctively to the clock. It was five minutes to eight. Dinner would be served in five minutes, and one minute later, if the bomb was timed accurately, the reservoir would blow up.

Several of the pilots nodded to him, from which he a.s.sumed that the success of his morning's reconnaissance had been made public property. Some were in semi-flying kit, and from s.n.a.t.c.hes of conversation that he overheard he gathered that they had been detailed for a bombing raid which was to leave the ground shortly before midnight.

'Going to bomb the palm-trees at Sidi Arish,' he thought. 'Well, I -' His pleasant soliloquy ceased abruptly, and he stiffened instinctively as a sound floated in through the open windows. It was the low, musical cadence of an aero-engine rapidly approaching.

Aeroplanes were common enough at Zabala, but not those carrying Rolls-Royce engines.

Biggles recognized the deep, mellow drone, and knew that a British machine was coming towards the camp, probably an F.E. 2D.* So did some of the German pilots, and there was a general stampede towards the door.

'Put those lights out,' yelled von Faubourg, who appeared from nowhere, so to speak, without his tunic.

Now we see der fun,' said Brandt, who stood at Biggles' elbow. 'Watch for der fireworks.'

Biggles started, for he, too, was expecting some fireworks-on a big scale, from the direction of the reser-Two-seater 'pusher' biplane with the engine behind the pilot and the gunner in the forward c.o.c.kpit.

voir-but he did not understand Brandt's meaning. 'Fireworks?' he queried, as they stared up into the darkness.

'Der new battery on der hill is of der grandest-so! straight from der Western front, where it makes much practice. Watch der Englander in der fireworks-ha!'

The exclamation was induced by a searchlight that suddenly stabbed in to the night sky from somewhere behind the hangars; it was followed immediately by another that flung its blinding shaft upward from a point of vantage near the top of the hill.

The pilot of the British machine, as if aware of his peril, pushed his nose down for more speed-a move that was made apparent to the listeners on the ground by the sudden increase of noise. Still visible, but with the searchlights sweeping across the sky to pick it up, it seemed to race low across the back of the fort and then zoom upwards. A hush fell on the watchers as its engine cut out, picked up, cut again, and again picked up.

Biggles felt the blood drain from his face as he recognized the signal. 'Dear goodness, it'

s Algy,' he thought, and itched to tell him to clear off before the searchlights found him; but he could only stand and watch helplessly.

A babel of excited voices arose from the German pilots as the nearest searchlight flashed for a fleeting instant on the machine, lost it, swept back again, found and held it. An F.E.

2D stood out in lines of white fire in the centre of the beam. The other lights swung across and intensified the picture. Instantly the air was alive with darting flecks of flame and hurtling metal from the archie battery on the hill which, with the cunning of long experience, had held its fire for this moment.

Bang-whoof . . . bang-whoof bang-whoof .. .

thundered the guns as the British pilot, now fully alive to the danger, twisted and turned like a snipe to get out of the silent white arms that clung to him like the tentacles of an octopus.

A sh.e.l.l burst almost under the nose of the F.E., and a yell of delight rose from the Germans. 'I told you to watch der fireworks,' smiled Brandt knowingly, with a friendly nudge at Biggles, and then clutched at him wildly to prevent himself from falling as the earth rocked under their feet. It was as if the hill had turned into a raging volcano. A sheet of blinding flame leapt upwards, and a deep throated roar, like a thunderclap, almost shattered their ear-drums.

Simultaneously both searchlights went out, and a ghastly silence fell, a stillness that was only broken by the sullen plop-plop-plop of falling objects. Then a medley of sounds occurred together: yells, shrill words of command, and the rumble of falling masonry; but above these arose another noise, one that caused the Germans to stare at each other in alarm. It was the roar of rushing waters.

Biggles, who had completely forgotten his bomb in the excitement of watching the sh.e.l.ling of the F.E., was nearly as shaken as the others, but he was, of course, the only one who knew exactly what had happened.

Some of the officers darted off to see the damage, while others, discussing the explosion, drifted in to dinner, and Biggles, saying nothing but doing his best to hear the conversation, followed them. Some were inclined to the view that the explosion had been caused by a bomb dropped from the aeroplane, while others scouted the idea, pointing out that the machine had not flown over the hill while it had been under observation, or if it had flown over it before they were aware of its presence, then the delay between then and the time of the explosion was too long to be acceptable. Of von Stalhein there was no sign, and Biggles was wondering what had happened to him when the officers who had gone to the hill began to trickle back in ones Or twos.

They had a simple but vivid story to tell. One wall of the reservoir had been blown clean out, and the vast weight of the pent-up water, suddenly released, had swept down the hill-side carrying all before it. It had descended on the archie battery even before the gunners were aware of it and had hurled them into the village, where houses had been swept away and stores destroyed. The earth had been torn from under the guns, which had rolled down the hill and were now buried under tons of rock, sand, and debris. The Count was on the spot with every man he could muster, trying to sort things out and collect a provisional store of water in empty petrol-cans, goat-skins, or any other receptacle he could lay hands on.

Biggles heard the story unmoved. That he had succeeded beyond his wildest hopes was apparent, and he only hoped that Algy had seen and would therefore report the incident to Major Raymond, who would in turn notify General Headquarters and enable them to take advantage of it. Thinking of Algy reminded him of the signal and what it portended, but to look for the message in the darkness was obviously out of the question. That was a matter that would have to be attended to in the morning.

He sat in the mess reading his German grammar until the noise of engines being warmed up told him that the night bombers were getting ready to start, so he went out on to the tarmac to watch the preparations.

A strange sense of unreality came over him as he watched the bustle and activity inseparable from such an event. How many times had he watched such a scene, in France, from his right and proper side of the lines. The queer feeling of loneliness came back with renewed force, and in his heart he knew that he loathed the work he was doing more than ever; he would have much preferred to be sitting in the c.o.c.kpit of a bomber, waiting for the engine to warm up; in fact he would not have been unwilling to have taken his place in one of the Halberstadts, either as pilot or observer, and risk being shot down by his own people. It's all wrong,' he muttered morosely, as one by one the bombers took off, and the drone of the engines faded away into the distance. Lights were put out and silence fell upon the aerodrome; the only sounds came from the direction of the hill, where the work of salvage and repair was still proceeding. Feeling suddenly very sick of it all, he made his way, deep in thought, to his room, and without switching on the light threw himself upon the bed.

He suspected that he had dozed when some time later he sprang up with a start and stood tense, listening. Had he heard an aeroplane, or had he been dreaming? Yes! he could hear the whistling hum of an aeroplane gliding in distinctly now, and he crossed to the window in a swift stride, with a puzzled frown wrinkling his forehead. 'What the d.i.c.kens is going on,' he muttered. 'I never heard so much flying in my life as there is in this place.' The thought occurred to him that it might be one of the bombers returning with engine trouble and he waited for it to taxi in, but when it did not come his rather vague interest increased to wonderment.

As near as he could judge, the machine must have landed somewhere over the other side of the aerodrome, near the depression in which he had dropped the bomb and from which the mysterious machine had taken off earlier in the evening. 'That's the same kite come back home, I'll warrant,' he thought with increasing curiosity, and settling his elbows on the window-sill he stared out across the silent moon-lit wilderness. But he could see nothing like an aeroplane, and he was about to turn away when a figure came into view, walking rapidly. At first it was little more than a dim shadow, but as it drew nearer he saw that it was an Arab in burnous and turban. Was it the same man . . . ?

Breathlessly he watched him approach. He wanted to dash outside in order to obtain a clearer view of him in case he disappeared, so he continued watching from the window with a kind of intense fascination while his fingers tingled with an excitement he found difficult to control. It was a weird picture. The silent moonlit desert and the Arab striding along as his forebears had done in Biblical days.

It soon became clear that he was making for the fort. Biggles watched him disappear through the entrance, and a few seconds later a light appeared in one of the end windows.

He knew that there was no point in watching any longer. 'I've got to see inside that window,' he muttered, as he kicked off his shoes and stole out into the corridor.

With the stealth of an Indian, he crept along the back of the hangars until the black bulk of the old building loomed up in front of him. The light was still shining in the window, which was some six feet above ground-level, just too high for him to reach without something to stand on. He hunted round with desperate speed, afraid that the light would go out while he was thus engaged, and in his anxiety almost fell upon an old oil drum that lay half buried in the sand. He dragged it out by brute strength, and holding it under his arm, crept back to the wall of the fort, below the window from which streamed the shaft of yellow light. A cautious glance round and he stood the drum in place.

His heart was beating violently; he began to raise himself, inch by inch, to the level of the window. Slowly and with infinite care, he drew his eyes level and peeped over the ledge.

He was down again in an instant, struggling to comprehend what he had seen, almost afraid that the man within would hear the thumping of his heart, so tense had been the moment. At a large desk in the centre of the room von Stalhein was sitting in his shirt sleeves, writing. The inevitable cigarette smouldered between his lips and his monocle was in place. His sticks rested against the side of the desk.

Biggles' first reaction was of shock, followed swiftly by bitter disappointment, for it seemed that he had merely discovered von Stalhein's private office, and it was in this spirit that he picked up the drum, smoothed out the mark of its rim in the sand, and replaced it where he had found it. Then he hurried back towards his room. On reaching it he crossed to the window and looked out. The light had disappeared.

Slowly, and lost in a whirl of conflicting thoughts, he took off his uniform and prepared for bed. 'I wonder,' he said softly - 'I wonder.'

What he was wondering as he sank into sleep was if a slim dandy with a game leg could change his ident.i.ty to that of the brilliant, athletic, hard-riding Arab who was known mythically on both sides of the lines as El Shereef, the cleverest spy in the German Secret Service.

Chapter 7.

Still More Shocks Tired out, he was still in bed the following morning when he was startled by a peremptory knock on the door, which, without invitation, was pushed open, and the Count closely followed by von Stalhein strode into the room. If any further indication were needed that something serious was afoot, a file of soldiers with fixed bayonets who halted in the corridor supplied the deficiency.

Biggles sprang out of bed with more haste than dignity, and regarded the intruders with astonishment that was not entirely feigned.

all right, remain standing where you are,' ordered the Count curtly. 'Where were you last night?'

In my room, sir, where you yourself saw me,' replied Biggles instantly. 'After dinner-'

'Never mind that. Where were you between the time I left you and dinner time?'

I stayed here for a little while after you had gone, and then as the heat was oppressive-as you will remember I complained to you-I went out and sat on the tarmac.'

'Were you with anybody?'

'No, sir, by myself.'

In which case you have no proof that you were where you say you were.'

On the contrary, I think I can prove it to you, sir.' 'How?'

'Because while I was sitting there I saw Mayer land in a Halberstadt. You can verify that he did so. If I had not been there I could not have seen him.'

'That's no proof. Every one in the Mess knew that Mayer was flying,' put in von Stalhein harshly.

Biggles met his eyes squarely. 'I can tell you exactly how he behaved when he landed,' he said quietly. 'I couldn't learn that in the Mess.'

'Send for Mayer,' said the Count crisply.

There was silence for two or three minutes until he came.

'Can you remember exactly what was the first thing you did when you landed last night?'

asked the Count tersely.

Mayer looked puzzled.

'May I prompt his memory, sir?' asked Biggles. And then, looking straight at Mayer, he went on, 'You jumped out as soon as you reached the tarmac and walked back to the empennage* of the machine. You then tried the rudder as if it was heavy on controls.'

Mayer nodded. 'That's perfectly true; I did,' he agreed.

, 'All right, you may go,' barked the Count, and then turning to Biggles. 'Very well, then, we'll say you were on the tarmac,' he said grimly, 'in which case you may find it hard to explain how that found its way to the hill-side, near the reservoir.' He tossed a small gold object on to the table.

Biggles recognized it at once; it was his signet ring. It did not fit very well, and must have fallen from his finger while he was hunting for the gap in the wire. The most amazing thing was he had not missed it. To say that he was shaken as he stared at it, gleaming * General term referring to the tail unit of any aircraft-the tail plane, elevators, fin and rudders.

dully on the table, would be an understatement of fact. He was momentarily stunned by such a d.a.m.ning piece of evidence. For a period of time during which a man might count five he stared at it dumbfounded, inwardly horror-stricken.

In the deathly hush that had fallen on the room the match that von Stalhein struck to light his cigarette sounded like a thunderclap.

Biggles' brain, which for once seemed to have failed, like an aero engine when the spark is cut off, suddenly went on again at full revs. He dragged his eyes away from the unmistakable evidence of his guilt and looked at the Count with a strange expression on his face, aware that von Stalhein's eyes were boring into him, watching his every move.

I think I can explain that, sir, although you may find it hard to believe.'

'Go on, we are listening.'

'Leffens must have dropped it there.'

'Leffens!'

'Yes, sir, he had my ring.'

'Had your ring!' The Count's brain was working slowly, and even von Stalhein dared not interrupt.

'Yes, sir; I lent it to him yesterday morning. I met him on the tarmac, just as he was getting into his machine. He told me he had forgotten his ring, and that it would mean bad luck to go back for it. So as he was in a hurry I lent him mine.'

'But I saw you wearing yours only yesterday evening,' snapped von Stalhein, unable to contain himself.

Not mine, Leffen's,' answered Biggles suavely. 'He suggested I had better borrow his during his absence, and told me that it was lying on his dressing-table. I fetched it and have worn it ever since. I've been meaning to report the matter.'

'Then why aren't you wearing it now?'

I always take it off to wash, prior to going to bed,' returned Biggles easily.

He took Leffens' ring from the drawer of his dressing-table where he had placed it when he returned from the flight in which he had shot down the rightful owner of the ring. He tossed the tiny circle of gold on to the table with the other.

Another ghastly silence fell in which he could distinctly hear the ticking of his wrist-watch. In spite of the tension his brain was running easily and smoothly, with a deadly precision born of dire peril, and he looked at his interrogators, whose turn it was to stare at the table, with an expression of injured dignity on his face.

Strangely enough, it was the Count who recovered himself first, and he looked back at Biggles half apologetically and half in alarm. 'But your ring was found on the hill-side,'

he said in a half whisper. 'Surely you are not suggesting that Leffens had any hand in the blowing up of the reservoir?'

Biggles shrugged his shoulders. He saw von Stalhein feeling in his pocket and knew he was searching for the incriminating bullet, so he went on quickly. 'I am not suggesting anything, sir, nor can I imagine how it got there. I only know that for some reason Leffens disliked me; in fact, he tried to kill me.'

'Tried to kill you?' The Count literally staggered.

'Yes, sir; he dived down at me out of the sun and tried to shoot me down. It was a clever attack, and unexpected; some of his bullets actually hit the machine. He zoomed back up into the sun and disappeared, but not before I had seen who it was. There is just a chance, of course, that he mistook my machine for an authentic enemy aircraft.' Biggles could see that even von Stalhein was impressed.

'But why in the name of heaven didn't you report it?' cried the Count aghast.