"Nothing," said Hercule Poirot with feeling. "Do I not have cause to know it? Never shall I forget the killing of Lord Edgware. I was nearly defeated - yes, I, Hercule Poirot - by the extremely simple cunning of a vacant brain. The very simple minded have often the genius to commit an uncomplicated crime and then leave it alone. Let us hope that our murderer - if there is a murderer in this affair - is intelligent and superior and thoroughly pleased with himself and unable to resist painting the lily. Enfin - but continue."

Once more Mr Goby applied himself to his little book.

"Mr and Mrs Banks - who said they were at home all day. She wasn't, anyway! Went round to the garage, got out her car, and drove off in it about 1 o'clock. Destination unknown. Back about five. Can't tell about mileage because she's had it out every day since and it's been nobody's business to check.

"As to Mr Banks, we've dug up something curious. To begin with, I'll mention that on the day in question we don't know what he did. He didn't go to work. Seems he'd already asked for a couple of days off on account of the funeral. And since then he's chucked his job - with no consideration for the firm. Nice, well-established small pharmacy it is. They're not too keen on Master Banks. Seems he used to get into rather queer excitable states.

"Well, as I say, we don't know what he was doing on the day of Mrs L.'s death. He didn't go with his wife. It could be that he stopped in their little flat all day. There's no porter there, and nobody knows whether tenants are in or out. But his back history is interesting. Up till about four months ago - just before he met his wife, he was in a Mental Home. Not certified - just what they call a mental breakdown. Seems he made some slip up in dispensing a medicine. (He was working with a Mayfair firm then.) The woman recovered, and the firm were all over themselves apologising, and there was no prosecution. After all, these accidental slips do occur, and most decent people are sorry for a poor young chap who's done it - so long as there's no permanent harm done, that is. The firm didn't sack him, but he resigned - said it had shaken his nerve. But afterwards, it seems, he got into a very low state and told the doctor he was obsessed by guilt - that it had all been deliberate - the woman had been overbearing and rude to him when she came into the shop, had complained that her last prescription had been badly made up - and that he had resented this and had deliberately added a near lethal dose of some drug or other. He said