Donaldson toiled up the dark staircase leading to Barstow's laboratory. To him it was as though he were fighting his way through deep water reaching twenty fathoms above his head. The air was just as cold as green water; it contained scarcely more life. He felt the same sense of clammy, lurking things, unknown things, such as crawl along the slimy bottoms where rotting hulks lie. He was impelled here by the same sort of fascination which is said to lead murderers back to their victims, yet it seemed to be the only place where he would be able to think at all. It was getting back to the beginning--to the source--where he could start fresh. It was here, and here alone, that he could write his letter to her. Perhaps here he could make something out of the chaos of his thoughts. When he reached the top of the stairs, he paused before the closed door. He did not expect Barstow to be in. He hoped that he was not. He did not wish to face him to-day. To-morrow perhaps--but he realized that if Barstow had gone on his proposed vacation he would not be back even then. That did not matter either. The single thing remaining for him to do was to make Elaine understand something of what his life had meant, what she had meant in it, what he hoped to mean to her in the silent future. That must be done alone, and this of all places was where he could best do it. The mere thought of his room at the hotel was repulsive to him. He listened at the door. There was no sound--no sound save the interminable "tick-tock, tick-tock" which still haunted him through the pulse beats in his wrists. He reached forward and touched the knob; listened again, and then turned it and pressed. The door was locked. But it was a feeble affair. Barstow had made his experimental laboratory in this old building to get away from the inquisitive, and half of the time did not take the trouble to turn the key when he left, for there was little of value here. He knocked on the chance that Barstow might have lain down upon the sofa for a nap. Again he waited until he heard the "tick-tock, tick-tock" at his wrists. Then, pressing his body close to the lock, he turned the knob and pushed steadily. It weakened. He drew back a little and threw his weight more heavily against it. The lock gave and the door swung open.