"The sun was just setting."

"Curious," said Poirot again. "And you, Dr. Gerard, when did you see the body?"

"Not until the following day. At nine A.M., to be precise."

"And your estimate of the time death had occurred?"

The Frenchman shrugged his shoulders. "It is difficult to be exact after that length of time. There must necessarily be a margin of several hours. Were I giving evidence on oath I could only say that she had been dead certainly twelve hours and not longer than eighteen. You see, that does not help at all!"

"Go on, Gerard," said Colonel Carbury. "Give him the rest of it."

"On getting up in the morning," said Dr. Gerard, "I found my hypodermic syringe—it was behind a case of bottles on my dressing table." He leaned forward. "You may say, if you like, that I had overlooked it the day before. I was in a miserable state of fever and wretchedness, shaking from head to foot, and how often does one look for a thing that is there all the time and yet be unable to find it! I can only say that I am quite positive the syringe was not there then."

"There's something more still," said Carburv. "Yes, two facts for what they are worth and they mean a great deal. There was a mark on the dead woman's wrist—a mark such as would be caused by the insertion of a hypodermic syringe. Her daughter explains it as having been caused by the prick of a pin—"

Poirot stirred. "Which daughter?"

"Her daughter, Carol."

"Yes, continue, I pray you."

"And there is the last fact. Happening to examine my little case of drugs I noticed that my stock of digitoxin was very much diminished."

"Digitoxin," said Poirot, "is a heart poison, is it not?"

"Yes. It is obtained from digitalis purpurea—the common foxglove. There are four active principles—digitalin—digitonin—digitalein—and digitoxin. Of these, digitoxin is considered the most active poisonous constituent of digitalis leaves. According to Kopp's experiments, it is from six to ten times stronger than digitalin or digitalein. It is official in France—but not in the British Pharmacopoeia."

"And a large dose of digitoxin?"

Dr. Gerard said gravely: "A large dose of digitoxin thrown suddenly on the circulation by intravenous injection would cause sudden death by quick palsy of the heart. It has been estimated that four milligrams might prove fatal to an adult man."

"And Mrs. Boynton already suffered with heart trouble?"

"Yes; as a matter of fact, she was actually taking a medicine containing digitalis."

"That," said Poirot, "is extremely interesting."

"D'you mean," asked Colonel Carbury, "that her death might have been attributed to an overdose of her own medicine?"

"That—yes. But I meant more than that. In some senses," said Dr. Gerard, "digitalis may be considered a cumulative drug. Moreover, as regards postmortem appearance, the active principles of the digitalis may destroy life and leave no appreciative sign."

Poirot nodded slow appreciation. "Yes, that is clever—very clever. Almost impossible to prove satisfactorily to a jury. Ah, but let me tell you, gentlemen, if this is a murder, it is a very clever murder! The hypodermic replaced, the poison employed being one which the victim was already taking—the possibilities of a mistake—or accident—are overwhelming. Oh, yes, there are brains here. There is thought—care—genius."