Milo said he was unable to think of anything, but he would certainly look.
The constable had to open up for them, because the door at the stern had been fitted with a fresh lock. Milo's German-made padlock had been stripped down and examined at the forensic lab. Pressed by Diamond for their findings, the scientists had reported no flaw in the mechanism. No sign, even, of tampering. It was described as a high-security close-shackle padlock. The locking mechanism provided over six million key variations, bearing out the manufacturers' claim that each padlock they sold in Britain had a unique key pattern.
Diamond had been over the narrowboat and its security arrangements many times in his mind without deducing how the body had been placed there, so this extra inspection wasn't embarked upon with much confidence. The murder of Sid Towers was becoming his own locked room mystery, his Gordian knot. If Milo Motion had spoken the truth, the facts were indisputable:
1. Milo locked the boat when he left it.
2. The key never left his person.
3. The keys fitted that padlock and no other. There was no second key.
4. The only other point of entry to the cabin was the door at the fore end, and this was bolted from the inside.
5. The padlock was still in position when Milo returned to the boat with Wigfull. He had opened it with the key and discovered the corpse of Sid Towers in the cabin.
Each time he looked for a flaw in the logic, Diamond was forced back to that qualifier: if Motion had spoken the truth. The hardware, surely, was foolproof; the human assurances had to be tested further.
The two men dipped their heads to enter the cabin, now stripped of its carpet.
"I want you to think hard and long," Diamond told Milo. "Do you keep anything in here that might have been used as a weapon? Some ornament, perhaps, like a heavy beer mug or a paperweight?"
Milo thought for a moment and shook his head. "Books are about the heaviest things in here. You couldn't kill someone with a book, could you?"
"It would take something heavier than those," Diamond admitted, eyeing the shelves of detective stories. "A really big dictionary might do the job."
"Can't help. I manage without one."
"Lucky for you. Good speller, are you?" he asked companionably. Putting the man at his ease might encourage him to talk more freely about the evening of the murder.
"Correct spelling was part of the education when I grew up."
"Mine, too." Diamond switched to a confiding mode. "I was at grammar school, but I never fully mastered the spelling. Bit of a handicap, because they deducted marks in every subject, and it all went on a weekly report card. There was a ritual on Saturday mornings called 'slackers' parade'-a painful encounter with the deputy head-and I was a regular on it. Then one of the English masters taught me the trick of avoiding words like necessary. You can always write needful instead. Good advice. So the next time, that's what I did-and still finished up on the slackers' parade. Pity he didn't warn me needful has only one / at the end. Tell me, what's the attraction of detective stories?"
Milo blinked and frowned, derailed by the unexpected admission of frailty by the man he'd come to regard as the embodiment of authority.
"I've never understood what people see in them," Diamond went on. "True crime, yes, I can read with pleasure. Fiction I can't."
"I suppose it's the not knowing."
"The what?"
"The not knowing… until the end," Milo explained.
"Not knowing who did it?"
Milo relaxed slightly. "That's true of some books, certainly, but not all. There are other things the reader is keen to discover these days. I mean, some books tell you right off who the villain is. There's the fascination of not knowing whether he gets away with the crime, or whether the good chap survives. There's much more emphasis on character these days, but there's always an element of surprise in the best mysteries. You should attend one of our Bloodhound meetings."
"I may end up doing that. Would you mind stepping into the kitchen, or the galley, or whatever you call it?"
"You'd like a coffee?" said Milo.
"No, Mr. Motion." Abruptly he was the investigator again. "We're checking for a possible murder weapon. Remember?"
"Ah."
Nothing was missing from the galley that Milo could recall.
"You appreciate the importance," Diamond said to take the edge off his sharp remark. "The choice of weapon can tell us if the murder was planned or was just a response to something unexpected. Did the killer bring a weapon here with murder in mind, or was it just a matter of snatching up the first thing that came to hand?"
"I follow you," said Milo.
"But you can't help me?"
"On this matter, no."
"While we're here, let's go over the business of the padlock," Diamond continued. "I know you've been through it so many times you could say it in your sleep, but something else needs to be explained, doesn't it? The boat was totally secure, according to you, and yet a murder took place in here."
"Don't you think I'd have told you by now if I knew the answer?" Milo said with injured virtue. "It's utterly beyond my understanding. What is more, they got in twice. Someone must have broken in earlier to put the stamp inside my copy of John Dickson Carr."
"There's no evidence that anyone broke in." Diamond was swift to correct him. "If they had, we might have an explanation. Not one of the doors or windows was interfered with. Nothing was broken."
"What happened then? They couldn't have had a key. Mine is the only one in existence."
"That isn't true, is it? There's the spare one you dropped in the canal."
"If you want to nitpick to that degree, yes."
"How long ago did you lose it?"
"Last year. I told you."
"Exactly when, Mr. Motion?"
Milo sighed. "Toward the end of the summer. It must have been September."
"Can you recall the circumstances? I daresay it caused you some annoyance."
"Well, it did. I lost my car keys at the same time."
"So we're talking about a bunch-on a ring?"
"Yes."
"Did you try to recover them?"
"It happened after dark,"' Milo explained, tugging at his beard as if the whole episode was painful to recall. "If you must know, I was the worse for drink. Pretty unusual for me. A night out at the Cross Guns."
"The pub at Avoncliff?"
"Yes. Do you know it? Gorgeous on a summer evening. I had the boat tied up at one of the moorings just above the pub, that stretch of the canal before the aqueduct. Treated myself to a meal and a few beers, and when I got back-"
"Alone?"
"Yes. I opened up and stumbled a bit pulling open the door. The damned keys slipped out of my hand and over the side. Bloody annoying, but I knew I had spares for all of them, so it could have been worse."
"Next morning, did you try and get them out?"
He shook his head. "Hopeless. They would have sunk into the mud."
"Did you mention this to anyone else?"
"I may have done to the people in the next boat. Can't remember, frankly."
"What about the Bloodhounds? Would you have mentioned it to them?"