But a trick of the light, a flick and a flash.

‘I’m alright, love. You don’t need to fuss. It’s only three floors.’

Petra turned to where Helena was watching her. ‘No, Mom, not you… I…’ She turned back to the bicycles and boxes. ‘Where…’ Petra pushed between the bikes in case the woman had collapsed there while she’d turned to Helena. But she was gone – she was probably embarrassed or self-conscious; she must have hurried out the front door while Petra’s back was turned.

‘God, I hope she’ll be alright,’ Petra said.

‘Who’s this now?’ Helena said.

‘The woman who was standing here, Mom. Jeez, did you see her face?’

Helena stared at her. ‘Nah, love. I didn’t see anyone.’

4 Petra left Suki’s car in the bay behind Needful Things before walking home. Usually when she borrowed it she’d keep it until the morning, but tonight Suki was heading to the Leisure Dome events venue at Birmingham airport for a night of queue fieldwork at a Reprise Girls concert.

One of Suki’s side hustles was a freelance queue-research collective she’d formed called Line Logic Limited, whose services were commissioned by a range of events promoters, shopping malls, casinos, transport franchises and the like. Their methods were based on a mixture of social psychology and mind-control techniques. At a concert like tonight’s, Suki and her colleagues would use a variety of diagnostic tools to record customer behaviour as they queued for entrance, for snacks, for the toilets, and at the parking lots and train stations afterwards. In this case, the aim was to try to balance customer experience with cost-effectiveness, but everyone knew that at concerts, customer experience was by far the lighter end of that balance. As evidenced every summer, music fans of a certain age and deprived of regular sunlight would pay hundreds of pounds to crawl through piss-and-beer-saturated mud to be in the general vicinity of a band they liked. You had to be more careful of customer experience where attendance was voluntary, or if a conference could be moved to another venue next year.

The work had originated at a psychology student club at university but Petra had no idea why Suki still did it. She certainly didn’t need the money, and it wasn’t that she needed to get out of the house. Suki went out a lot, had a wide circle of what she called her ‘frenemies’. Maybe it was just stimulating fun, and more so because it was something the Barlow clan hadn’t laid out for her.

Other times, and for other clients, she’d played a more insidious role. She’d be tasked with deliberately cutting queues at banks, pushing down the up escalator at the Bullring shopping centre, farting in lifts, singing loudly on trains. It was clear she enjoyed these jobs more, and Suki would regale Petra with preparatory talk on the Milgram experiments, the pros and cons of serpentine queues, queuer distraction, misdirection and redirection, and the polite flesh-eating zombie sheep effect (Suki had probably made this term up for Petra’s benefit). She thought back on Helena’s performance at the hospital earlier – she’d be a great fit if Suki ever needed any more fieldworkers. She could earn some pocket money being her embarrassing self.