'Five units,' bleated the other.

Rage's jaw creaked as he grimaced with rage. 'Barely sufficient to complete drilling,' he rasped. 'The rockets are installed, Toba. Inform me as soon as your operations here are concluded.'

'Command accepted.'

As the Navigator strode away, the rig blared into life again beginning the crucial final stage of the bore.

On the clifftop above, two figures knelt in the sand.

'They've started drilling again,' Jamie mouthed. 'We still have a chance...'

The sound of the drilling starting up again brought a profound sigh of relief from the Doctor as he grabbed the next plastic sheet filled with sand from Kando at the mouth of the tunnel and handed it to Zoe, who emptied it onto the huge pile growing ever larger in the middle of the shelter. At least the race to intercept the seeding trigger was not yet lost, but there was so little time left...

'How much further have you got, Teel?'the Doctor called into the vibrating darkness of the runnel.

'A little more than my own length...' came the brave young Dulcian's m.u.f.fled reply.

The Doctor did a quick mental calculation and turned to Zoe. 'Still a long, long way to go...' he frowned. 'Teel, coem out and rest now. Zoe's turn.'

When Teels' feet appeared. the Doctor and Kando reached into the hole and pulled him out. The exhausted Dulcian, covered in dirt and sweat, staggered to a bench and collapsed gratefully. Armed with Jamie's dirk gripped between her teeth, be clambered into the tunnel and dragged herself into the hot, throbbing gloom by walking on her dhows and knees.

When she reached the face, she pulled the plastic sheet out of her belt and spread it out as best she could behind her. The vibration of the drilling rig caused a constant trickle of sand to run into her eyes as she dug desperately away at the crumbling sandstone ahead, sc.r.a.ping the loose sand past her body and onto the sheet so that the others could empty it periodically in the shelter. The task was agonisingly slow and awkward and it was horrifying to feel that the shuddering tunnel might collapse at any moment and trap her.

Eventually she stopped to rest her aching arms a moment. All at once the tunnel shook with a series of violent shocks. Zoe's heart almost froze as the tunnel started cracking all around her.

In the shelter, the Doctor had dived for the periscope.

'Jamie and Kully have attacked the rig!' he shouted, cheering as the two Quarks careered sideways and the rig itself toppled over, belching smoke and sparks. 'Zoe, the drilling's stopped!'

'So will the tunnelling if they're not careful...' muttered Zoe, digging away again for all she was worth.

Peering through the eyepiece, the Doctor watched Rago rush into view escorted by three Quarks. Expertly he lip-read the hurried dialogue between the two Dominators.

'See what damage your "harmless" aliens are doing with their primitive explosives? Now we must surely destroy them,' Tuba insisted.

Rago flung out his huge hand. 'Replace the rig and continue. I shall personally pursue and destroy these saboteurs,' he retorted.

Seeing his revenge denied him, Toba sullenly concurred. As Rago set off towards the gorge, accompanied by the three Quarks, Toba struggled to re-position the rig over the target. The Doctor said nothing as he re-joined the others at the mouth of the tunnel, but his gentle face betrayed increasing anxiety about the fate of Jamie and the diminishing likelihood of thwarting the Dominators in their evil purpose.

Unaware of Rago's intentions, Jamie and Kully slid helter-skelter down into the canyon on their way back to the shelter. No sooner had they reached the bottom than they were dismayed to see Rago and his Quarks advancing inexorably along the floor of the canyon towards them.

Whooping with delight, Kully started preparing a bomb, but Jamie grabbed his arm and yanked him roughly back up the slope. Their progress was painfully slow as the sand gave under them, forcing them to take three steps for every one gained in height.

Rage's eyes burned with contempt as he ordered his squad to attack. Three pairs of probes were trained in deadly concentration on the desperate fugitives crawling up the slope like wasps trying to escape from a jar of treacle. Huge scars were gouged in the slopes and bluffs as the Quarks fired simultaneously, but miraculously neither was. .h.i.t.

'Recharge force units,' Rago commanded. 'Report failure'

The robots whirred and sparked intermittently.

'Reserves below minima,' one of them announced.

Rago spat viciously. 'Toba is responsible for this entire fiasco. Quarks, quantise aggregate pulses. Single discharge.

Destroy them.'

Just as Jamie and Kully reached the top of the canyon, a savage tearing noise split the air around them. Kully gasped and choked and then uttered a terrible scream of agony. Jamie seized his wrist just in time to prevent him from rolling back into the gorge and hauled his dead weight up over the edge and onto the plateau.

'We're safe now, Kully...' he panted. 'the Quarks can't climb up here.'

Kully's face had gone a ghastly yellow and his teeth were chattering with shock. 'Something's happened...my arm... leg's gone cold.. can't move arm now... better leave me behind...'

Jamie put his arm protectively round Kully's paralysed shoulder. 'Nonsense. Ye'll be right as ninepence in a wee while.'

Peering over the edge, Jamie realised that Rago had ordered his Quarks to scale the longer but gentler slope at the end of the canyon. Despite their depleted power reserves, they were making good progress. If they reached the plateau, he and the wounded Dulcian had no chance at all.

Jamie quickly counted the remaining phials of chemicals stuck around the top of his sock. Then were four. 'One each...' he muttered, setting the phials upright in the sand and prising the box of silver pills out of Kully's frozen hand. 'Hang on, Kully...' he urged, dropping a pill in each phial and frantically jamming in the stoppers.

'Four... five... six...' He picked the phials up. 'Seven...

eight...' He leaped to his feet. 'Nine...' He threw the four phials together like a brace of daggers. They flew into the canyon and landed in an arc at the feet of Rago and the Quarks.

There were four sharp thunderclaps. Jamie saw the robots scatter in all directions, reeling and tottering, their probes firing indiscriminately into the air and at each other, and their distress signals bleating feebly. Two of them blew each other up and the third almost hit Rago before bursting into flames.

'Ye'll no dominate Jamie MacCrimmon...' the young Highlander yelled down at the scorched and tattered figure lying amidst the wreckage of his Quarks.

As Rago clambered awkwardly to his feet, Jamie hoisted Kully onto his shoulders and set off across the plateau towards the clifftop that overhung the ruin.

If they met any Quarks now, they were done for...

With Kando valiantly taking her turn in the tunnel, Zoe was manning the periscope while the Doctor and Teel emptied sheetful after sheetful of sand onto the heap which was now almost touching the ceiling.

'Toba's got the drill working again,' Zoe reported. 'We can't have much time left, Doctor.'

The Doctor glanced at the mound of excavated sand.

'We must be nearly through to their shaft by now,' he murmured hopefully.

'It feels very close...' Kando reported faintly, as she pushed another load of sand towards the tunnel-opening with her feet.

'So near and yet so far...' the Doctor mused, helping Teel with the sheet.

At that moment, the trap-door thudded open and Kully suddenly sprawled onto the mound and slid stiffly to the floor. Jamie jumped in after him and heaved the hatch shut before slithering down beside him. Briefly, Jamie explained what had happened since the intrepid pair had set out on their vital mission.

'Luckily for Kully, the Quarks' power-levels were low...'

he concluded.

Zoe and the Doctor had made the casualty as comfortable as possible in the sand.

'It's my left side... it's paralysed...' he moaned.

The Doctor gently took hold of Kully's left wrist. 'Can you move your fingers at all?' he asked.

Kully shut his eyes and screwed up his face with effort His fingertips twitched a little, then his thumb stirred.

The Doctor smiled encouragingly. 'You are are lucky. I think it's only temporary.' lucky. I think it's only temporary.'

Kully managed a plucky grin. 'Don't worry about me, Doctor. What about the tunnel?' he murmured feebly.

'Thanks to you and Jamie we've almost finished it.'

Zoe gave a startled shout. 'Doctor, they've stopped drilling again!'

The Doctor rushed to the periscope just in time to see the battered figure of Rago limping up to Toba as the Quarks began dismantling the rig. Once again he deciphered their brief exchange, his own lips moving as he read theirs.

'The centre bore is completed, Navigator.'

'Good, I shall enjoy absorbing this miserable planet and its insignificant creatures, Toba. Bring the seeding trigger immediately. No more delays.'

There was just the faintest of smiles on Toba's grim visage as he glanced at his superior's undignified disarray before marching obediently away.

Jamie had already taken Kando's place at the tunnel face and he was sending out load after load of sand. 'Any sign of that bore shaft yet, Jamie?' the Doctor yelled anxiously as he returned to help the others.

'Och no. The roof keeps caving in though...' came the faint reply out of the foetid darkness.

They worked like beavers in the hot, stifling atmosphere of the cramped shelter, while Kully lay on the mound and kept up a brave repartee of encouragement. Hours seemed to pa.s.s, but everyone had lost all sense of time, endlessly repeating the same automatic movement, over and over again. And very soon them would be no more s.p.a.ce in the shelter to dump the eternal flow of sand...

Then all at once Zoe grabbed the periscope handles.

'The Dominators are coming back... they've got the device!' she cried.

The Doctor dropped the heavy plastic sheet he was carrying and peered into the binocular. He watched as Toba carefully handed the seeding trigger still in its curious spiky gla.s.s sh.e.l.l to Rago. The Dominators' faces were bathed in a lurid pink glow as they conferred over the centre bore target.

'Recall all operational Quarks. Prepare the craft for departure and rendezvous with Fleet. Inform Fleet Leader that refuelling orbit may commence on schedule.'

'Command accepted.'

Rago cradled the weirdly glowing device almost lovingly in his ma.s.sive gloves. 'I shall insert the seeding trigger.

You will return and synchronise the perimeter target projectiles immediately. Soon we shall see this planet and its species burst asunder.'

The Doctor's face clouded with indignation as he mouthed the Dominator's terrible words. He watched Toba stride purposefully away to prepare the rockets and then focused the periscope on Rago. The Navigator was pressing the tips of the bristling gla.s.s spikes in an apparently random sequence and with each movement the pink glow intensified. Eventually the gla.s.s sh.e.l.l came apart and Rago delicately withdrew the opalescent egg within.

'Criticality minus beta.'

Unable to watch any longer, the Doctor closed his eyes and leaned his forehead against the periscope 'We're too late...' he sighed dejectedly. 'We've failed...'

'We're through, Doctor!'

Spinning round, the Doctor saw Jamie's dirt-streaked smile filling the tunnel mouth.

'Only a wee bit too far to the left,' Jamie cried as he clambered out. 'Not bad at all.'

The Doctor whipped back to the periscope. Rago was lending over the borehole, the seeding trigger poised in his outstretched hands.

In a single bound, the Doctor flung himself at the tunnel and vanished into the darkness.

Zoe flew to the periscope. She uttered a cry of despair.

Rago's hands were empty. 'It's gone... we missed it,' she said, trifling a sob of disappointment.

There was a long silence. Jamie, Zoe, Kando, Teel and Kully stared glumly at one another and then turned anxiously towards the tunnel.

After a while, they heard m.u.f.fled mutterings and then a frantic scrambling. Gradually the Doctor emerged feet first from the narrow opening. He stood up and then turned to face the astonished group. He was holding the huge egg as though it were a bomb.

'You did it.' whispered Zoe.

'So, we are saved,' Kando burst out, with a brilliant smile.

'Not quite saved...' murmured the Doctor, moving in slow motion as if the slightest shock could he disastrous.'

We still have to neutralise it.' With infinite care, he turned the glowing device over and over in his trembling hands.

Then he looked at them, appalled. 'It's sealed... completely sealed...' he gasped. 'I can't open it.'

They all stared at him helplessly.

'Ye mean it was all for nothing?' Jamie exclaimed bitterly. 'Are we going to he blown to smithereens after all?'

The Doctor nodded. 'I'm afraid so, Jamie. Unless we can get it away from Dulkis immediately..

Teel and Kando were kneeling beside Kully. Their three faces were overcast with incredulity and anguish.

Jamie and Zoe gazed at the Time Lord with barely concealed resentment.

Suddenly the Doctor grinned mischievously.

'Whatever's the matter with you all?' he demanded, weighing the lethal object almost nonchalantly in one hand, his eyes beginning to twinkle. 'Teel and Kando, you take Kully to the capsule near the saucer, get back to the Capitol and warn them that there might be a little earthquake and a volcano or two popping up here and there. Jamie and Zoe, you go straight back to the TARDIS and wait there for me...'

He was interrupted by a chorus of protest.