“Thank you. Yes, the problems of heredity have an extraordinary fascination, even for a layman like myself. However, I haven’t come here to air my ignorance of your country, but to try and fill out some of the blanks in my own. About this O’Callaghan business—”

“I am extremely sorry to hear of the result of the autopsy,” said Roberts formally. “It is terribly distressing, shocking, an irreplaceable loss.” He moved his hands nervously, gulped, and then added hurriedly: “I am also exceedingly distressed for more personal reasons. As anæsthetist for the operation I feel that I may be held responsible, that perhaps I should have noticed earlier that all was not well. I was worried, almost from the start, about his condition. I said so to Sir John and to Thoms.”

“What did they answer?”

“Sir John was very properly concerned with his own work. He simply left me to deal with mine, after, I think, commenting in some way on my report. I do not remember that Thoms replied at all. Inspector Alleyn, I sincerely hope you are able to free Sir John from any possibility of the slightest breath of suspicion. Any doubt in that direction is quite unthinkable.”

“I hope to be able to clear up his part in the business as soon as the usual inquiries have been made. Perhaps you can help me there, Dr. Roberts?”

“I should be glad to do so. I will not attempt to deny that I am also very selfishly nervous on my own account.”

“You gave no injection, did you?”

“No. I am thankful to say, no.”

“How was that? I should have imagined the anæsthetist would have given the camphor and the hyoscine injections.”

Roberts did not speak for a moment, but sat gazing at Alleyn with a curiously helpless expression on his sensitive face. Alleyn noticed that whenever he spoke to Roberts the doctor seemed to suppress a sort of wince. He did this now, tightening his lips and drawing himself rigidly upright in his chair.

“I—I never give injections,” he said. “I have a personal and very painful reason for not doing so.”

“Would you care to tell me what it is? You see, the fact that you did not give an injection is very important from your point of view. You did not see the patient while he was conscious and so—to be frank—could hardly have poured hyoscine down his throat without someone noticing what you were up to.”