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." The Principal, disturbed in the midst of changing her travelling costume, listened with amazement to her insistent pupils' excited account. "This must be investigated immediately," she declared. "Dulcie, fetch a candle and matches, and you must both accompany me to this cave. You say Gerda has gone on there alone?" Miss Birks took the affair gravely. She appeared very much concerned, even alarmed. She hurried off at once with the girls to the kitchen-garden. They led the way down the narrow staircase cut in the cliff, and across the beach and over the rocks. At the entrance to the cave they both uttered a sharp exclamation, for Gerda stood there in an attitude of hesitation, as if unable to make up her mind whether to enter or no. She turned red, and white, and then red again to the tips of her ears when she saw that she was discovered, but she offered no explanation of her presence there. She did not even speak. "Girls," said Miss Birks, "I think it is highly desirable and necessary that we should follow this passage into the room which I am told is beyond. Deirdre, you go first, with this candle, then Dulcie--Gerda, give me your candle, and walk just in front of me."