"And is she a girl or a spook?" added Dulcie.

"Spooks don't drink tea. She must be alive," said Deirdre. "I wonder if Miss Birks knows about her?"

"I guess we'd better not divulge the secret!" chuckled Dulcie.

"What would Miss Birks say to us for trespa.s.sing in the kitchen-garden?--particularly when she's away."

"We should get into a jolly row!" agreed Deirdre.

"We shall all three get into one as it is if we don't go back quickly,"

observed Gerda.

Rather conscience-stricken, the chums obeyed her suggestion. They were fortunate enough to slip from the kitchen-garden without being observed, and hoped their escapade would not be discovered. After tea they hurried to make up arrears of practising, but Gerda, evading the vigilance of Mademoiselle, gave an excuse to Miss Harding and absented herself from preparation. Stealing very cautiously from the house she dived through the shrubbery and ran out on to the warren. Casting many a hasty glance behind her to see if she were observed, she hurried along till she reached the little point above St. Perran's well where a rough pile of stones made a natural beacon, easily visible from the sea or from the beach below. Taking her handkerchief from her pocket she tied it to a stick, which she planted at the summit of the pile. Waving in the breeze it was a conspicuous object. She watched it for a moment or two, then walked back along the cliff with the drooping air of one who is almost ready to collapse after meeting a great emergency.

"It was a near thing--a near thing!" she muttered to herself. "Suppose they'd met? Oh, it's too horrible! It was too risky an experiment, really! I hope my danger signal's plain enough. I must get up early to-morrow and take it down before anyone from the school sees it. It'll be difficult with those two in the room--but I'll manage it somehow.

Fortunately they're both sound sleepers!"

CHAPTER XVIII

An Alarm

That same evening an extraordinary thing happened. It was the custom for gla.s.ses of milk, dishes of stewed fruit, and plates of bread and b.u.t.ter to be placed on the table in the dining-hall about eight o'clock. This was done as usual, but when the girls arrived for supper they found a large proportion of the bread and b.u.t.ter had vanished. At first the suspicion fell on Spot, the fox-terrier, but the cook pleaded an alibi on his behalf, proving that he had been in the kitchen the whole time; also, the rifled plates were in the middle of the table, so no dog could have purloined their contents without knocking over gla.s.ses, or disturbing spoons and forks.

"I'm afraid it's a two-legged dog," said Miss Harding gravely. "The French window was open, and it would be easy for anyone to walk in and help himself. I'm glad nothing more valuable was taken. I wish Miss Birks were here! It's most unfortunate it should happen on the very evening she's away."

The incident gave cause for serious apprehension. Miss Harding made a most careful round of the house before bedtime, to see that all bolts and shutters were well secured. Though she would not betray her alarm to the girls, she was afraid that a burglary might be committed during the night. Both she and Mademoiselle kept awake till dawn, listening for suspicious footsteps on the gravel outside. All was as usual, however, in the morning; there were no evidences of attempts to force locks or windows, and no trace of the mysterious thief who had taken the bread and b.u.t.ter. Mademoiselle reported indeed that she had again heard the curious sounds which for some nights past had disturbed her. She had risen and patrolled the house, and had come to the unmistakable conclusion that they issued from the barred room. The closed chamber was as much a riddle to teachers as to girls, so Miss Harding merely shook her head, and recommended Mademoiselle to tell her experiences to Miss Birks as soon as the Princ.i.p.al returned.

At five o'clock that afternoon Elyned Hughes came running downstairs with a white, scared face. She solemnly averred that, when pa.s.sing the door of the mysterious room, she had heard extraordinary noises within.

"It was exactly like somebody moving about and frying sausages. I smelled them too!" she declared.

The report was in part confirmed by several other girls, who pledged their word that they heard stealthy movements when they listened at the barred door.

"Are you absolutely certain, or is it only mice?" queried Gerda. "We've so often fancied things."

"Mice don't clink cans, and strike matches, and clear their throats!"

retorted Rhoda.

"But you may have thought it sounded like that."

"I couldn't be mistaken."

"Somebody's there, beyond a doubt," said Agnes.

"Perhaps it's a ghost?" queried Elyned.

"It's nothing supernatural this time, I'll undertake to say--whatever may have made the noises before."

"It ought to be enquired into," declared Doris. "Miss Birks ought to insist on having the bars taken down, and seeing what's going on."

"Oh, no, no! It's best to leave things as they are."

Gerda was looking white and upset and spoke almost hysterically.

"Do you expect the ghost to bolt in amongst us the moment the door is unlocked?" mocked Rhoda.

"No, of course, I'm not so silly! But it's often better to let well alone."

"Mrs. Trevellyan is still away, so Miss Birks couldn't ask her to have the bars taken down now," volunteered Betty Scott.

"So she is," exclaimed Gerda, with an air of relief.

"Ah! You're afraid of the ghost," repeated Rhoda. "I'm more inclined towards the burglar theory. In the circ.u.mstances, I think Miss Birks would be quite justified in making an investigation, even without Mrs.

Trevellyan's permission."

"I shouldn't wonder myself if Miss Birks called in the police," said Betty Scott.

The girls were in a ferment of excitement over the affair. Deirdre and Dulcie felt that in view of yesterday's discovery they had a strong clue to the mystery. They hesitated as to whether they ought at once to tell Miss Harding, but, as Miss Birks was expected home within an hour or two, they decided it was better to wait till they could deliver their news at head-quarters.

Gerda, during the whole day, had been very abstracted and peculiar in her manner. She was nervous, starting at every sound, and seemed so preoccupied with her own thoughts that she often took no notice when spoken to.

"What's wrong with the Sphinx?" commented Deirdre. "She's absolutely obsessed."

"Yes, I can't make her out. She's disturbed in her mind. That's easy enough to see. There's something queer going on in this school. I hope she's not mixed up in it."

"We'd decidedly better watch her. After all that's happened before, one can't trust her in the least. Until Miss Birks is safely back in the house I feel we oughtn't to let Gerda out of our sight. Who knows what she may be going to do, or whom she's in league with?"

Coupled with the mysterious happenings of last night and to-day, Gerda's palpable uneasiness gave strong grounds for suspicion. The chums watched her like a couple of detectives. They were determined to warn Miss Birks directly on her return. Meanwhile nothing their room-mate did must escape their notice. They were to perform a duet at the musical examination, therefore they had the extreme felicity of doing their practising together. For the same half-hour Gerda was due at the instrument in the next room. They waited to begin until they heard the first bars of her "Arabesque". At the same moment came from the hall the sounds of the bustle occasioned by Miss Birks's arrival home. Deirdre and Dulcie looked at one another in much relief.

"She'll just be downstairs again by the time we've finished practising, and then we'll go straight and tell her," they agreed.

I am afraid neither in the least gave her mind to the piano.

Mademoiselle, had she been near, would have been highly irate at the wrong notes and other faults that marred the beauty of their mazurka.

Both girls were playing with an ear for the "Arabesque" on the other side of the wall.

"She's stopped!" exclaimed Dulcie, pausing in the middle of a bar. "Now, what's that for, I should like to know? I don't trust you, Miss Gerda Thorwaldson."

But Deirdre was already at the window.

"Look! look!" she gasped. "Gerda's off somewhere!"

The window of the adjacent room was a French one, and the girls could see their schoolfellow open it gently and steal cautiously out on to the lawn. She glanced round to see if she were observed, then ran off in the direction of the kitchen-garden. In a moment the chums had thrown up the sash of their window and followed her. All their old suspicions of her had revived in full force; they were certain she was in league with somebody, and for no good purpose, and they were determined that at last they would unmask her and expose her duplicity. They had spared her before, but this time they intended to act, and act promptly too.

Gerda opened the gate of the kitchen-garden as confidently as if she were not transgressing a rule, and rushed away between the strawberry beds. Pilfering was evidently not her object, for she never even looked at the fruit, but kept straight on towards the end where the horse-radish grew. Keeping her well within sight, the chums went swiftly but cautiously after. She stood for a moment on the piece of waste ground that bounded the cliff, looked carefully round--her pursuers were hidden behind a tree--then plunged down the side of the rock and out of sight. Deirdre and Dulcie each drew a long breath. The conclusion was certain. Without doubt she must be going to pay a visit to the cave which communicated with the mysterious chamber. Whom did she expect to find there?

"To me there's only one course open," declared Deirdre solemnly. "We must go straight to Miss Birks and tell her this very instant."