"Bit of a risk to take, wasn't it? Fiddling about with a door-lock when anyone might have seen him?"
"Whoever committed this murder took the hell of a lot of risks, if you ask me. If I remember rightly, Miss Herriard was seen outside the door in her dressinggown."
"You don't think this was a woman's job, sir, do you?" asked the Sergeant incredulously.
"Might have been. Don't you go getting a lot of silly ideas into your head about women! I've known some who'd have put a cageful of tigers to shame. One thing seems pretty certain: Nathaniel wasn't expecting to be stabbed. There are no signs of any struggle, not even a chair pushed out of place. He was taken unawares, and he didn't suspect the murderer of meaning to injure him."
"Come to think of it," objected the Sergeant, "that doesn't point particularly to Miss Herriard. He wouldn't suspect any of the people in the house, would he?"
"He'd suspect them fast enough if they started tampering with the lock of his door," said Hemingway. "No, it looks as though the murderer came in in the natural way, all aboveboard and open, stabbed the old man, and went out again, locking the door behind him by some means which we haven't yet discovered. And somehow I don't believe it."
The Sergeant saw the frown on his superior's brow, and asked: "Why not, sir?"
"I've got a feeling it didn't happen that way. What did the murderer lock the door for at all? It's no use saying, to bamboozle the police, because it isn't good enough. If you find a corpse in a locked room, what's the inference?"
"Suicide," replied the Sergeant promptly.
"Exactly. And if you want a murder to look like suicide you don't first stab the victim in the back, and next remove the knife. There was no idea of making this look like suicide, so the locked door doesn't add up at all." He looked carefully at the plate in the jamb, which had been torn away. "In fact," he said, "I'm beginning to wonder whether the door ever was locked."