"Ah Ling. No one else."
"No one else? What about the doctor?"
"But that was afterwards."
"Of course it was afterwards. There was no trace of powdered opium in the curry served to Mr. Paynter, but acting in obedience to the suspicions Dr. Quentin had aroused, the old man eats none of it, and preserves it to give to his medical attendant, whom he summons according to plan. Dr. Quentin arrives, takes charge of the curry, and gives Mr. Paynter an injection—of strychnine, he says, but really of yellow jasmine—a poisonous dose. When the drug begins to take effect, he departs, after unlatching the window. Then, in the night, he returns by the window, finds the manuscript, and shoves Mr. Paynter into the fire. He does not heed the newspaper that drops to the floor and is covered by the old man's body. Paynter knew what drug he had been given, and strove to accuse the Big Four of his murder. It is easy for Quentin to mix powdered opium with the curry before handing it over to be analysed. He gives his version of the conversation with the old man, and mentions the strychnine injection casually, in case the mark of the hypodermic needle is noticed. Suspicion at once is divided between accident and the guilt of Ah Ling owing to the poison in the curry."
"But Dr. Quentin cannot be Number Four?"
"I fancy he can. There is undoubtedly a real Dr. Quentin who is probably abroad somewhere. Number Four has simply masqueraded as him for a short time. The arrangements with Dr. Bolitho were all carried out by correspondence, the man who was to do locum originally having been taken ill at the last minute."
At that minute, Japp burst in, very red in the face.
"You have got him?" cried Poirot anxiously.
Japp shook his head, very out of breath.
"Bolitho came back from his holiday this morning—recalled by telegram. No one knows who sent it. The other man left last night. We'll catch him yet, though."