human
The same ingenious lock, made for the plotters by a skilled mechanician (whom they had reason to trust), shot out its poisoned needle at the first turn of the latchkey in his hand. As for the poison, it, too, was supplied by a trusted one---one who had something to gain and vengeance to take as well. As the mechanician specialised in lock-making, so did the chemist employed specialise in poisons. The one he chose out of his repertory had two virtues: first, it began to stop the heart's action only after coursing through the blood for twenty or thirty minutes. Anything quicker might have struck down the victim in front of the door and put the police on the right track. Secondly, the poison's effect on the heart couldn't be detected by post-mortem, but presented all the symptoms of status lymphaticus, enlargement of the thyroid gland and so on. As for the lock, the second turn of the key caused the needle to retire; and for a further safeguard, an almost invisible stop, resembling a small screw-head, could hold the needle permanently in place inside the lock, so that the door might be opened by a latchkey and the existence of a secret mechanism never suspected, except by one who knew how to find it. The mechanism is in working order still, ready for use again, in case Miss Grace Callender should change her mind and decide to marry.
gpt
Who is it you are accusing, Lord John?