“Okay, but not because I want to help you. I’m only telling you because it supports my argument,” she said, gliding the mop across the floor and sloshing Robin’s shoes in a way that was almost certainly deliberate. “The Five and him went through on a private boat. He had the keys to the gate across the front of the canal tunnel. He opened the tunnel before he went to get the boat at the mooring site about a mile out of Marsden. He piloted the boat through the tunnel. There was no third party, no bogeyman—him. He was the only one who could’ve done it.”

“What about the abandoned tunnel? The one you take the van through?”

She looked almost impressed. “You’ve done your homework—well done. That tunnel was locked up tight. We had trouble with kids getting in the tunnel a few years back—the whole thing is fenced off either side but they used to burrow under. So we poured concrete along the fence boundary. Those gates are unlocked with a keycard—a keycard that was locked up in here on that day. No one else could have done it.”

“Did Matthew have a key to the Visitor Centre?”

“You’re thinking he took the keycard and replaced it somehow. Benefits of it being a computer system on the gate—you can see when the gate was unlocked. It wasn’t—at all—that day. And anyhow, he took the tunnel gate key the day before. Visitor Centre was locked.”

“So Matthew couldn’t have used the abandoned tunnel to move the bodies of his friends?”

“He could have accessed the tunnel through the multiple cut-throughs in the canal tunnel but he couldn’t have got out.”

“What about the other side of the canal tunnel? The train tunnels?” He was saying and hearing tunnel so much, the word was starting to lose all meaning.

“There’s no real easy way to get to the live train tunnels. There are no paths or whatnot. And even if you did get in there—well, they’re called ‘live’ for a reason.”

Robin grew silent and watched Martha go up and down the floor. She paused and nodded to Robin to move and he stepped back, up the step into the doorway to the table area. “You’ve said that no one else could have done it, but by your description, it doesn’t seem like Matthew could have done it either. What do you think happened?”

Martha stopped, leaning on the mop. “I thought he drowned them. Then the divers came back and they weren’t in the water. Then I thought he’d hidden them in the abandoned tunnel. And that search was a bust too. Then I just sort of stopped wondering.”