“She’s a psychotherapist. Her website says she specializes in relationship and familial issues.” Seeing that Sam was about to object, Simon said, “I know—it doesn’t mean anything. Except . . . she’s chosen to devote her life to helping people who hate the people they’re supposed to love. Maybe she did too—hated her husband, wanted him dead.”

“I think that’s . . . a stretch, simply from her choice of profession,” Sam said after a few seconds.

“Well, I’m not wrong about the missing word,” said Simon, keen to return to safer ground. “What might come after the ‘than’?”

Sam shrugged helplessly. “There must be infinite possibilities. How can we narrow it down?”

“A person’s name,” said Simon. “‘He is no less dead than . . . Fred.’ Let’s say it’s that, for the sake of argument. What would that mean? That he’s more dead than Fred? Or the same amount dead? There’s no such thing as more dead,” he answered himself.

“If it’s a name—Fred or Mary or whatever—that could suggest other victims,” said Sam. “Each one no less dead than the one before.”

“Yeah.” Simon nodded slowly. “I like that.” A bit. Not a lot, not enough to stick with it. “Or how about another meaning: ‘He is no less dead than he was while alive’? No, that’d make better sense if it was ‘no more dead.’”

“Simon, it could be anything.”

“I know that, and I know your ‘shall-we-just-give-up?’ voice.”

“No, I wasn’t—”

“We need to think of every single thing it might be, anything and everything that could conceivably come after ‘than.’” Simon walked over to the desk, nearly tripping over the knife sharpener on his way. It was black, heavy and could have doubled as a doorstop. “Too much and too many to be meaningless,” he muttered, “but maybe only one meaning . . . Yeah. One.”

“Explain?” said Sam.

“All the things the killer’s left us are different routes to the same information—different prompts. Whatever that shit on the wall means, whatever it means that he could easily have stabbed Blundy with the knife in the photo but chose instead to suffocate him with a knife and some tape . . . he’s given us lots of clues, but it’s not like a crossword, where each one’s designed to give you a different answer. Imagine a crossword with numbers one to twenty across and numbers one to twenty down and in all forty cases it’s the same nine-letter word we’re trying to guess.”

“Why nine letters?” Sam asked.

“Random,” said Simon impatiently. “Call it eight or ten if you like. Point is, the crossword creator really wants us to guess the answer—this ten- or nine- or eight-letter word’s important to him. He thinks we need to know it, but he also thinks we’re stupid—unlikely to twig unless he gives us lots and lots of clues.”

“So . . . ?”