“That is the complicated part of this business; the rest of it depends on two simple accidents. Mottram went to bed rather early; he was in an excited frame of mind, and determined to steady himself with a sleeping draught. The watch, the studs, were only symptoms of that fussiness we all feel on the eve of a great adventure. I suppose he borrowed a match from Brinkman to light his gas with. But it was a clear night; there was no need of light to go to bed by. But just at the last moment—a fateful moment for himself—he did light the gas; perhaps he wanted to read a page or two of his novel before turning in.
“The rest of the story could be more easily told upstairs. I wonder if you would mind all coming up into the actual room? It makes it so much easier to construct the scene if you are on the spot.”
The whole party applauded this decision. “This is what is called an object-lesson, in the education of the young,” observed Mr. Pulteney. “The young like it; they are in a position to hack one another’s shins when the teacher’s back is turned.”
When they reached the bedroom, Bredon found himself falling into the attitude of a lecturer. “The guide,” murmured Angela, “taking a party round the ruins of the old dungeon. Scene of the ’orrible crime. Please pay attention, gentlemen!”
“You see how the gas works in here,” began Bredon. “There’s the main tap, we’ll call it A, which controls the whole supply. Tap B is for the bracket; tap C leads through the tube to the standard lamp. It doesn’t matter leaving tap B or tap C on as long as tap A is turned off.
“When Mottram went up to bed, tap B and tap C were both open, but tap A was properly turned off. Mottram took no particular notice of the disposition of taps; he turned on one tap at random, tap A. Then he lit his match, and put it to the bracket, which naturally lit. He then immediately threw the match away. We know that, because we found the match, and it was hardly burned down the stalk at all. Meanwhile, of course, he had also allowed the gas to escape through the tube into the standard lamp; it never occurred to him to light this. The standard was at the other end of the room, close to the open window; the slight escape of gas did not, unfortunately for him, offend his nostrils. Brinkman told me, and it is probably true, that Mottram had not a very keen sense of smell. After a minute or two, feeling ready to go to sleep, he went up to the taps again, and forgot to reverse the process he had gone through before. Instead of turning off the main tap, A, he carelessly turned off tap B. And the light on the bracket obediently went out.
“That is the lesson of a fingerprint. Tap A was stiff, and Mottram left a mark when he turned it on; he would have left another if he had turned it off. He did not; he turned off tap B, which works at a mere touch, and of course he left no mark in doing so. There, then, lies Mottram; the sleeping draught has already taken effect; the wind gets up, and blows the window to; tap A is still open, and tap C is still open; and through the burner of the standard lamp the acetylene is pouring into the room.
“Brinkman is not a late sleeper. The Boots, who is the earliest riser in this establishment, tells me that Brinkman was always awake when he went round for the shoes. On Tuesday morning Brinkman must have woken early, to be greeted by a smell of gas. It may have crept in through his window, or even come up through the floor, for the floors here are full of cracks. Once he had satisfied himself that the escape was not in his own room, he must have thought of the room below. When he reached the lower passage, the increasing smell of gas left him in no doubt. He knocked at Mottram’s door, got no answer, and rushed in, going straight across and opening the window so as to get some air. Then he had time to turn round and see what was on the bed. There was no doubt that he was too late to help.”
“Did he know it was accident?” asked Eames. “Or did he think it was suicide?”
“I think he must have known it was accident. And now, consider his position. Here was Mottram, dead by accident. There up in London was Mottram’s codicil, willing half a million to the Diocese of Pullford. And that codicil had not been meant to become operative. It had been made only for the purposes of the test. And now, through this accident, the codicil, which did not represent Mottram’s real wishes, had suddenly
