Anna thanked the usher, sat down, and stared straight ahead for ten minutes as the auditorium started to fill behind her all the way from the stalls up to the gods. Then, as the house lights began to fade and the orchestra tested their instruments, she got up and walked down the stairs next to her seat.

Knox and Bennett were nodded through the front doors of the opera house by a Watcher dressed as a ticket checker.

Knox had changed into a dark grey Henry Poole suit he kept in his office, and Bennett was wearing the simple black shift dress Sarah had given her. It fitted her, which, as she was almost a foot shorter than the director general’s wife, suggested it had either been borrowed from a younger relative or bought specially for her. She liked the dress, but she didn’t like the narrow-heeled patent-leather pumps that had also been produced for her—she’d been in them for less than an hour and they were already rubbing her feet.

‘You ever been here before?’ Bennett asked Knox as they scanned the audience festooned in fur and jewellery in the entrance hall.

‘Once or twice,’ Knox replied. ‘But never to such a starry affair.’

His suit was expensive and well tailored, but surrounded by men in dinner jackets and bow ties he felt conspicuously underdressed.

Knox usually preferred to watch his ballet at Sadler’s Wells in Clerkenwell. Its productions were more experimental, and its seats were cheaper. Ironically for Nureyev, the great ex-Soviet dancer had decided he wanted to come to London at the beginning of a revival of Les Noces, a traditional ballet about a Russian peasant wedding by Igor Stravinsky and Bronislava Nijinska. More ironically for Knox, it had been quickly agreed that Nureyev would instead perform in a one-night revival of Card Game, an abstract, playful work also scored by Stravinsky and choreographed by George Ballanchine that had been the opening dance in a mixed programme the Royal Opera House’s ballet company had recently staged.

‘Well,’ Bennett said, lowering her voice as she kept looking round the crowd, ‘none of these people look like assassins to me.’

‘No,’ Knox agreed, ‘they don’t.’

‘So what do we do?’

‘Trust the Watchers, the police, and Sarah to deal with the crowd while we look everywhere else.’

More and more people had arrived in the few minutes they’d been inside. Then a bell rang out over the sea of people and they all began to surge towards the doors and staircases that would lead them into the auditorium. Everyone apart from Knox, Bennett, and the other MI5 and police staff.

In a few minutes the entrance hall was almost empty. Knox looked towards a Met officer he recognised from Congress House, who shook his head at him.

‘Maybe he’s not coming after all,’ Bennett said.