“In the second place, when he took the precaution of drawing up a new will he neglected to sign it overnight. Brinkman, I suppose, pointed out to him that if any fatal accident occurred—say a motor accident—the codicil leaving the half-million to the Bishop would be perfectly valid. To avoid this danger they must have drawn up a new will, and if Mottram had signed this overnight his death would have made it valid. As it was, for some reason—probably because Brinkman himself was drawing it up (I think the writing is Brinkman’s) late on Monday night—the will was never signed and was useless.
“In the third place, he did something overnight which he ought to have left till the next morning. He not only wrote his confidential letter to the Bishop but he went out with Brinkman to the gorge and posted it—put it on the ledge ready for the Bishop to find next morning. He did not mean to go into the gorge at all the next morning. He would start out on the way to it, say, at eight, and at ten minutes past eight Brinkman, driving the car, would pick him up on the road. From the side of the road they could throw over Mottram’s hat, possibly, and they could slide his rod down the rocks, so as to make it appear that he had been there. (Brinkman, in this way, would establish an alibi; he could not be supposed to have murdered Mottram in the gorge.) But it was not safe to let the letter drop in this casual way; therefore the letter must be planted out overnight. There was no great danger of its premature discovery; in any case, Mottram put it rather out of sight on a ledge so high up that only a tall man would see it, and only if he was looking about him carefully.
“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.
The three taps as Brinkman found them