"When did you first suspect John Cavendish?" I asked, after a minute or two.
"Did you not suspect him at all?"
"No, indeed."
"Not after that fragment of conversation you overheard between Mrs. Cavendish and her mother-in-law, and her subsequent lack of frankness at the inquest?"
"No."
"Did you not put two and two together, and reflect that if it was not Alfred Inglethorp who was quarrelling with his wife--and you remember, he strenuously denied it at the inquest--it must be either Lawrence or John. Now, if it was Lawrence, Mary Cavendish's conduct was just as inexplicable. But if, on the other hand, it was John, the whole thing was explained quite naturally."
"So," I cried, a light breaking in upon me, "it was John who quarrelled with his mother that afternoon?"
"Exactly."
"And you have known this all along?"
"Certainly. Mrs. Cavendish's behaviour could only be explained that way."
"And yet you say he may be acquitted?"
Poirot shrugged his shoulders.
"Certainly I do. At the police court proceedings, we shall hear the case for the prosecution, but in all probability his solicitors will advise him to reserve his defence. That will be sprung upon us at the trial. And--ah, by the way, I have a word of caution to give you, my friend. I must not appear in the case."
"What?"
"No. Officially, I have nothing to do with it. Until I have found that last link in my chain, I must remain behind the scenes. Mrs. Cavendish must think I am working for her husband, not against him."
"I say, that's playing it a bit low down," I protested.
"Not at all. We have to deal with a most clever and unscrupulous man, and we must use any means in our power-- otherwise he will slip through our fingers. That is why I have been careful to remain in the background. All the discoveries have been made by Japp, and Japp will take all the credit. If I am called upon to give evidence at all"--he smiled broadly-- "it will probably be as a witness for the defence."
I could hardly believe my ears.
"It is quite en regle," continued Poirot. "Strangely enough, I can give evidence that will demolish one contention of the prosecution."
"Which one?"
"The one that relates to the destruction of the will. John Cavendish did not destroy that will."