“But when,” asked Angela, “did Dr. Roberts inject the hyoscine?”

“I think soon after the patient was put on the table. The screen over the chest would hide his hands.”

“I see.”

“After the reconstruction Roberts wouldn’t leave us alone. He hung about in the theatre, intent, of course, on keeping me away from the cruet. Fox, bless his heart, rumbled this ruse and staged a bogus telephone call. He saw I wanted to be rid of Roberts. As soon as we were alone I fell on the cruet, and, after a nerve-racking fumble, unearthed the syringe. Eureka! Denouement! Fox nearly had a fit of the vapours.”

“So you arrested him there and then!” cried Angela.

“No. No, I didn’t. For one thing I hadn’t a warrant and for another—oh, well—”

Alleyn rested his nose on his clasped hands.

“Now what’s coming?” asked Angela.

“I rather liked the little creature. It would have been an unpleasant business pulling him in there. Anyway, I went off and got a warrant, and Fox and Boys accompanied him home. They watched him carefully in case he tried to give himself the coup de grâce, but he didn’t. When I arrested him he had, I believe, a sudden and an appalling shock, a kind of dreadful moment of lucidity. He fought us so violently that he seemed like a sane man gone mad, but I believe he was a madman gone sane. It only lasted a few minutes. Now I don’t think he cares at all. He has made a complete confession. He’s batty. He’ll have to stand his trial, but I think they’ll find that the nut in the cruet-stand is not the only one loose. It may even be that Roberts, recognizing the taint of madness in himself, felt the eugenic urge the more strongly and the need for eliminating the unfit. In that point of view there is precisely the kind of mad logic one would expect to find in such a case.”

“If it hadn’t been for the matron’s trip, would you never have got him?” asked Nigel.

“I think we should—in the end. We should have got his history from Canada and Australasia. It’s coming through now. When it’s complete I am pretty certain we shall find a series of deaths after anæsthetics given by Roberts. They will all prove to be cases where there were signs of hereditary insanity. I shouldn’t mind betting they correspond with the notches on the stethoscope—minus one.”

“Minus one?” asked Nigel.