Colwyn returned to his scrutiny of the young man at the alcove table, and he and his companion studied him intently for some time in silence. But the young man, for the moment, was comparatively quiet, gazing moodily through the open window over the waters of the North Sea, an untasted sole in front of him, and an impassive waiter pouring out his coffee as though the spectacle of a young man sticking a knife into the table-cloth was a commonplace occurrence at the Grand Hotel, and all in the day's doings. When the waiter had finished pouring out the coffee and noiselessly departed, the young man tasted it with an indifferent air, pushed it from him, and resumed his former occupation of staring out of the window. "He seems quiet enough now," observed Colwyn, turning to his companion. "What do you think is the matter with him--shell-shock?" "I would not care to hazard a definite opinion on so cursory an observation," returned the other, in a dry, reticent, ultra-professional manner. "But I will go so far as to say that I do not think it is a case of shell-shock. If it is what I suspect, that first attack was the precursor of another, possibly a worse attack. Ha! it is commencing. Look at his thumb--that is the danger signal!" Colwyn looked across the room again. The young man was still sitting in the same posture, with his gaze bent on the open sea. His left hand was extended rigidly on the table in front of him, with the thumb, extended at right angles, oscillating rapidly in a peculiar manner. "This attack may pass away like the other, but if he looks round at anybody, and makes the slightest move, we must secure him immediately," said Colwyn's companion, speaking in a whisper. He had barely finished speaking when the young man turned his head from the open window and fixed his blue eyes vacantly on the table nearest him, where an elderly clergyman, a golfing friend, and their wives, were breakfasting together. With a swift movement the young man got up, and started to walk towards this table.