‘No. Well, there’s the difficulty.’

‘But why – why would anyone do this?’

‘I can think of a few reasons. It would be a big help if you could ask your mother about this, though, John. Whether she had the laptop running in mid-March. Whether any of her visitors expressed an interest in it.’

‘I – I’ll try.’ Bristow sounded very stressed, almost tearful. ‘She’s very, very weak now.’

‘I’m sorry,’ said Strike, formally. ‘I’ll be in touch shortly. ’Bye.’

He stepped back from the balcony and closed the doors, then turned to Wilson.

‘Derrick, can you show me how you searched this place? What order you looked in the rooms that night?’

Wilson thought for a moment, then said:

‘I come in here first. Looked around, seen the doors open. Didn’t touch ’em. Then,’ he indicated that they should follow him, ‘I looked in here…’

Robin, following in the two men’s wake, noticed a subtle change in the way that Strike was talking to the security man. He was asking simple, deft questions, focusing on what Wilson had felt, touched, seen and heard at each step of his way through the flat.

Under Strike’s guidance, Wilson’s body language started to change. He began to enact the way he had held the door jambs, leaning into rooms, casting a rapid look around. When he crossed to the only bedroom, he did it at a slow-motion run, responding to the spotlight of Strike’s undivided attention; he dropped to his knees to demonstrate how he had looked under the bed, and at Strike’s prompting remembered that a dress had lain crumpled beneath his legs; he led them, face set with concentration, to the bathroom, and showed them how he had swivelled to check behind the door before sprinting (he almost mimed it, arms moving exaggeratedly as he walked) back to the front door.

‘And then,’ said Strike, opening it and gesturing Wilson through, ‘you came out…’

‘I came out,’ agreed Wilson, in his bass voice, ‘an’ I jabbed the lift button.’

He pretended to do it, and feigned pushing open the doors in his anxiety to see what was inside.

‘Nothing – so I started running back down again.’

‘What could you hear now?’ Strike asked, following him; neither of them were paying any attention to Robin, who closed the flat door behind her.

‘Very distant – the Bestiguis yelling – and I turn round this corner and—’

Wilson stopped dead on the stair. Strike, who seemed to have anticipated something like this, stopped too; Robin careered straight into him, with a flustered apology that he cut off with a raised hand, as though, she thought, Wilson was in a trance.

‘And I slipped,’ said Wilson. He sounded shocked. ‘I forgot that. I slipped. Here. Backwards. Sat down hard. There was water. Here. Drops. Here.’

He was pointing at the stairs.

‘Drops of water,’ repeated Strike.

‘Yeah.’

‘Not snow.’

‘No.’

‘Not wet footprints.’