Robin found the choice of adjective callous.

‘Pushing someone over a balcony’s a spur-of-the-moment thing,’ said Strike, as though he had felt her inner wince. ‘Hot blood. Blind temper.’

He found Robin’s company satisfactory and restful, not only because she was hanging off his every word, and had not troubled to break his silences, but because that little sapphire ring on her third finger was like a neat full stop: this far, and no further. It suited him perfectly. He was free to show off, in a very mild way, which was one of the few pleasures remaining to him.

‘But what if the killer was already inside?’

‘That’s a lot more plausible,’ said Strike, and Robin felt very pleased with herself. ‘And if a killer was already in there, we’ve got the choice between the security guard himself, one or both of the Bestiguis, or some unknown person who was hiding in the building without anyone’s knowledge. If it was either of the Bestiguis, or Wilson, there’s no getting-in-and-out problem; all they had to do was return to the places they were supposed to be. There was still the risk she could have survived, injured, to tell the tale, but a hot-blooded, unpremeditated crime makes a lot more sense if one of them did it. A row and a blind shove.’

Strike smoked his cigarette and continued to scrutinise the front of the building, in particular the gap between the windows on the first floor and those on the third. He was thinking primarily about Freddie Bestigui, the film producer. According to what Robin had found on the internet, Bestigui had been in bed asleep when Lula Landry toppled over the balcony two floors above. The fact that it was Bestigui’s own wife who had sounded the alarm, and insisted that the killer was still upstairs while her husband stood beside her, implied that she, at least, did not think him guilty. Nevertheless, Freddie Bestigui had been the man in closest proximity to the dead girl at the time of her death. Laymen, in Strike’s experience, were obsessed with motive: opportunity topped of the professional’s list.

Unwittingly confirming her civilian status, Robin said:

‘But why would someone pick the middle of the night to have an argument with her? Nothing ever came out about her not getting on with her neighbours, did it? And Tansy Bestigui definitely couldn’t have done it, could she? Why would she run downstairs and tell the security guard if she’d just pushed Lula over the balcony?’

Strike did not answer directly; he seemed to be following his own train of thought, and after a moment or two replied:

‘Bristow’s fixated on the quarter of an hour after his sister went inside, after the photographers had left and the security guard had abandoned the desk because he was ill. That meant the lobby became briefly navigable – but how was anyone outside the building supposed to know that Wilson had left his post? The front door’s not made of glass.’