‘The match is about to begin, sir,’ a woman in a smart black jacket and a peaked cap told him as he pushed through the exit door. Foster kept walking, entering a walkway flecked by the last few excited stragglers heading towards their seats, and one man walking briskly away from them. He had a similar build to the guy who had followed him through the grounds after the quarter finals. He slipped out of the walkway and into the bright concourse, and skirted around the outside of Centre Court as Foster followed.

‘Hey!’ Foster called out.

The guy didn’t turn round. Instead, he broke his stride and began to run, gently at first, but as he sensed Foster following, he increased his speed. The milling crowd began to thicken, until eventually the concourse spread out onto the wide-open grass that the fans had christened ‘Henman Hill’ back in the Noughties and had rechristened ‘Murray Mound’ a decade later. A huge screen loomed over the lawn, and fans were watching the opening game of the final. The crowd was broiling and churning in the sunshine, a mass of elegant strawberry-munchers and Pimm’s-swillers and picnickers and raucous hen-dos, wearing everything from tennis whites to garish fancy-dress outfits. But each of them was focused on the action on the screen, and none of them made way when the guy Foster was chasing ploughed into them. He got stuck in the crowd, snared by the tangle of their limbs.

Foster was on him in seconds. He grabbed the man’s wrist and forced his arm behind his back. The guy yelled and a few onlookers backed off, the violence an unwelcome novelty inside the serenity of the All England Lawn Tennis Club.

‘Video this,’ the man yelled to anyone who would listen. His anger accentuated his east-London accent. ‘Grab your phones, put this on YouTube – seriously. This is police brutality, man.’

A few people turned to see what the commotion was all about, and the guy played up to them, yelling again as Foster forced his arm further up his back.

‘Who are you?’ Foster said, applying more pressure to the guy’s wrist. ‘Why did you run?’

‘I ran because you’re a cop,’ the guy said. ‘I’m not stupid. I could tell the way you looked at me that you’d rumbled me. So I legged it.’

‘Rumbled you doing what?’

As Foster twisted the guy’s arm harder still, his palm sprang open on reflex. A cascade of grubby entrance tickets fluttered down to the ground, spilling onto the lawn between the two men. There were murmurs in the crowd.

Shit!

‘You’re touting?’

‘Of course I’m fucking touting,’ the guy said, looking at the pile of spilled tickets. ‘I’m not going to deny it now, bro, am I?’

Shit! Wrong guy. In the London sunshine, a frost crept across Foster’s skin. This was the wrong time to be in the wrong place.