‘Bain?’ he said into the mobile. ‘I’ll meet you outside Costello’s flat.’

By the time Rebus got there, Bain had climbed the winding stairs and was standing outside Costello’s door.

‘I don’t think he’s home,’ Bain was saying, crouching down to look through the letter-box. A chill ran up Rebus’s spine, remembering what he’d seen when he’d peered into Devlin’s flat. Bain got to his feet again. ‘No sign of … Jesus Christ, man, what happened to you?’

‘Swimming lessons. I didn’t have time to change.’ Rebus looked at the door, then at Bain. ‘Together?’ he said.

Bain stared back at him. ‘Isn’t that illegal?’

‘For Siobhan,’ Rebus said simply.

They hit the door together on the count of three.

Inside, Bain knew what he was looking for: a computer. He found two in the bedroom, both of them laptops.

‘Claire Benzie’s,’ Bain guessed, ‘and either his own or someone else’s.’

The screen-saver had been activated on one computer. Bain accessed Costello’s ISP and opened the filing cabinet.

‘No time to try for a password,’ he said, almost to himself more than Rebus. ‘So all we can read are the old messages.’ But there were none to or from Siobhan. ‘Looks like he wipes as he goes,’ Bain said.

‘Or else we’re barking up the wrong tree.’ Rebus was looking around the room: unmade bed, books scattered across the floor. Notes for an essay on the desk next to the PC. Socks, pants and T-shirts spilled from the chest of drawers, but not from the top drawer. Rebus limped over, opened it slowly. Inside: maps and guidebooks, including one about Arthur’s Seat. A postcard of Rosslyn Chapel and another guidebook.

‘Right tree,’ he remarked simply. Bain got up, came to look.

‘Everything the well-dressed Quizmaster could need.’ Bain went to reach into the drawer, but Rebus slapped his hand away. ‘No touching.’ He tried sliding the drawer out further. Something was sticking. He took a pen from his pocket and dislodged it: an Edinburgh A–Z.

‘Open at the Botanics,’ Bain said, sounding relieved. If that’s where David Costello was, they’d have cornered him by now.

But Rebus wasn’t so sure. He was examining the rest of the page. Then he looked over towards Costello’s bed. Postcards of old gravestones … a small framed photo of Costello with Flip Balfour, with another headstone just coming into the frame. They’d met at a dinner party … breakfast next morning and then a walk in Warriston Cemetery. That was what Costello had told him. Warriston Cemetery was just across the road from the Botanic Gardens. Same page of the A–Z.