‘No. No way.’ He paused. Lying did not come naturally to him, never had – but this was for Wendy. ‘I need to talk to someone about what happened in the car park round the back . . .’

The guard rolled his eyes. Patrick noticed that the man’s stubble, crew cut, uniform and skin tone all seemed the same shade of grey. Perhaps it was the lighting. ‘If you’re a journalist, mate, you can sling your hook right now. I got a job to do here.’

‘I’m not, mate, honest. Thing is – that cop – she was my sister. Wendy. My kid sister . . .’

That got his attention. For the first time he looked sharply at Patrick, taking in his stained Vans and stubble, and the beginnings of the tears that Pat found no difficulty in summoning. ‘Oh. Right. Um . . . sorry to hear it. My condolences.’

Patrick scrubbed his sleeve across his face. ‘Thanks,’ he said in a cracked voice. ‘I heard she was in here before it happened. Meeting someone, but I don’t know who. The fucking police don’t have a clue and I can’t sit at home another day waiting for them to update me when they can’t seem to pull their fingers out. I mean, someone must’ve seen something!’

‘I feel for you . . . cock,’ said the guard. Two teenage boys loped down the stairs, one of them with his arm inside the front of his jacket. ‘Oi! You! No alcohol brought in, you know the rules. Give it here!’

The boy scowled and withdrew his arm to reveal the two open beer bottles he had hidden, which he handed reluctantly over.

‘If I catch you smuggling booze in one more time, you’re barred, you little toerag,’ the guard said.

Patrick watched the boys sulkily march down to the bowling lanes minus their contraband. ‘So, were you here that night?’ he asked the guard, who shook his head.

‘Nah, mate. Day off. Came in yesterday morning, all bleeding hell had broke loose. Manager handing over the CCTV. Cops interviewing all the staff.’

‘What about kids like those two?’ Patrick jerked his head down the stairs. ‘Obviously regulars, aren’t they?’

The guard leaned his elbows on the rail again and gestured down. ‘Cops identified one or two from the CCTV who were here when your sister come in. They’ve had a chat, apparently, but no-one had seen her before. Them two weren’t here at the time.’

‘Mind if I have a word?’

‘With them? Good luck to you. They’re so thick they probably don’t even know their own names.’

‘Could you, er, introduce me?’

Patrick had decided in advance this was the necessary level of obsequiousness. He didn’t want to plough in, in case the guard or the boys realised he was a cop – ‘the feds’, as kids called them these days. The feds! Like they lived in downtown Detroit, not suburban south-west London . . .

The guard appraised him, then shrugged. ‘If you want.’ They walked down the stairs together and over to the café area, where the two boys were examining a notice on the wall, which was advertising for part-time staff here at the Rotunda. They turned and looked up suspiciously at Patrick and the guard. The taller of the two held up his hands.

‘We don’t want no trouble. We’re just hanging out. Thinking of applying for a job here, actually.’

The guard rolled his eyes. ‘Good luck with that. This gentleman here wants a word. Show me you’re not both a waste of space and I might put in a word for you.’

A small, fascinated gaggle of teens had formed around them, bowling and flirting temporarily forgotten.

‘This is the brother of that cop that got murdered. So do something useful for once in your lives, and help him out, eh?’

Six or seven faces gaped in fascination and horror at their proximity to tragedy.

The taller of the two boys scrunched his nose like he’d smelled something nasty. ‘She was a fed. Why should we help someone catch the killer of a fucking cop?’

It took all Patrick’s willpower not to grab the kid by the front of his jacket and shove him against the wall.

‘Listen,’ he said, addressing the boy. ‘I’m not a huge fan of the police either. But Wendy wasn’t just a fed, as you call them. She was a human being. She was my sister.’

He glanced around, to make sure that none of his Met colleagues were in the bowlplex, before nodding gravely.

The group of teenagers stared at him, the tall boy hanging his head, one of the girls – a very pretty blonde with a nose stud, crop top and double-denim – punching the tall one on the shoulder and hissing, ‘You twat.’

‘So – were any of you here the night it happened, last Saturday?’ Patrick asked. ‘This is Wendy. Ever seen her in here?’ He took out his wallet and showed them a photo he’d printed off from Wendy’s Facebook page that morning – Wendy astride a pony, looking about twelve even though the photograph’s caption had been ‘On Holiday in the New Forest 2013’.

‘Ahhhh,’ sympathised an overweight girl whose bare muffin-top oozed over the waistband of her tight stonewash jeans, a silver belly bar almost completely hidden in the overhang. ‘She was ever so pretty.’

‘It didn’t happen in here, did it?’ the girl who’d punched the fed-hater asked. ‘My mum and dad won’t ever let me come here again if it did.’

‘No. It was round the back, opposite the bus station. But she was in here first to meet someone, so I want to know if she went there with them, or someone followed her?’

Blank faces all round.

‘Did any of you see her?’

They all shook their heads.

‘OK. If you weren’t here on Saturday, then you probably wouldn’t have. I don’t think she’d been here before. How about anyone else, your mates, who might have been? That guy’ – he pointed at the guard, who had drifted back to his vantage point halfway up the stairs – ‘says that you all hang out here every weekend. Why weren’t you here on Saturday?’

‘We were,’ chimed the prettier girl. ‘But the cops told us she – your sister – come in about 9.15 and we’ve usually gone home by then. Hardly any buses after half nine out towards Molesey.’

This was where Patrick and Gill lived, and he knew this to be true. ‘Do you all live on the 411 route, though? What about people who don’t – do they ever stay longer?’

The group all looked at one another, then the mixed-race boy said, ‘Well, yeah – the Feltham kids do, ’cos they can get the train back.’

‘Who are the Feltham kids?’ Patrick was dying to get his Moleskine out of his pocket.

The boy made a face. ‘We don’t like them. They only come here ’cos they got barred from Cineworld in Feltham.’

‘Really? Were any of them here when you left on Saturday?’

The blonde girl shook her head, making her poker-straight hair whip across into the eyes of her tubby mate, who jerked back.

‘Emily! That went in my eye!’ The two giggled self-consciously, then rearranged their faces back into sympathetic expressions.

Emily nudged her friend. ‘Wait – didn’t Foxy pull on Saturday? She was snogging the face off that chav from the Kennedy, remember?’

‘She left at the same time as we did, with him, didn’t she, so she wouldn’t have seen anything.’

The boys had started to lose interest and drift away back to their table in the café area, but it was the two girls that Patrick felt a spark of hope from.

‘Foxy? Who’s she?’

Emily shrugged. ‘Dunno. She’s always here, but we don’t know her real name. She knows all the Feltham boys, so I reckon she lives over that way, or goes to their school. I only know her ’cos she lent me her mascara in the bogs once.’

‘And she left with a boy around the same time as you did? I don’t suppose you’ve got her number, do you?’

To Pat’s disappointment they both shook their heads again. Anyway, he thought, it was probably nothing. There must have been loads of kids who were around that night and hadn’t seen anything.

‘Can I give you my number? Just in case you think of anyone else, or if Foxy shows up.’

Emily looked puzzled, as if something had just occurred to her. ‘Yeah, that’s weird actually.’ She pointed at the poster advertising the part-time jobs. ‘I thought she had an interview here today for one of them jobs. I’m sure that’s what she told me.’