He sat in his car nursing a can of Red Bull, watching the astounding number of people going in and out of the busy supermarket. He could people-watch all day; he’d always found it fascinating. The high from last night was still making him smile, but he had no time to lose. This time he needed a family of three. Two parents and one child: easier said than done. It was ambitious and he knew that, but he loved the challenge. He could discount anyone coming out with only one kid yet getting into a people carrier. There was a good chance they had more children stashed somewhere.

He started eating his sandwich, looking like any other man who hated shopping and was waiting for his wife to emerge from the store. Nobody gave him a second glance. Then a loud shout caught his attention. A boy of around ten years old came charging out through the shop doors, followed by a man and a frazzled-looking woman who was calling after the pair of them, pushing a shopping trolley. The boy ran straight across the car park and a woman driving a Mini Cooper had to slam on her brakes. She beeped her horn as the man ran past next.

Now this is interesting. He pushed the last of his sandwich into his mouth and sat up, tilting his rear-view mirror so that he could see the boy, who was now smacking the passenger-side door of a Mercedes B-Class parked a couple of cars behind him. The mother pushing the trolley mouthed sorry to the woman in the Mini, then scurried after who he assumed were her husband and son. The car’s hazard lights flashed and the boy threw the door open, clambering inside. The man, whose red face was a mask of fury, bent his head into the back of the car, but was pulled away by the woman. She shut the door and he watched her pleading with her husband to calm down. They were perfect: a chaotic, stressed-out family.

Starting his engine, he watched as the mother let go of the trolley and lowered herself into the passenger seat. She turned her head to talk to the boy, leaving her husband to pack the shopping into the boot and take the trolley back to the front of the store. If he had to guess, he would say the boy had some kind of learning difficulty or behavioural issues. Whatever it was, it didn’t matter. He would follow them home and see where they lived, judge if their house would be easy to get into or too difficult. Then he would spend a few days observing them, waiting to find out their routines. He needed to make sure it was just the three of them, because four or more wouldn’t fit the pattern. And it had to fit, one hundred per cent, for this to work.

He wondered how the police were dealing with the body they’d found this morning. Did they think it was connected to the woman from the start of the week or were they treating it as a separate incident? It didn’t really affect him; as long as he could continue with his plan everything would be okay.

The Mercedes accelerated rapidly in the direction of the drive-through McDonald’s. He wondered whether the treat was for the kid or to appease his father. This was a nuisance. He didn’t want to follow them through the drive-through; there might be cameras. He parked up outside Pizza Hut, his car facing the drive-through. As the Mercedes finally stopped at the window to collect the food order, he took a couple of quick snaps of the unsuspecting family inside. The boy, who had been having some kind of episode, had calmed down. He’d put his window down and he could see his face clearly – he was playing with a toy car. The young girl at the collection window passed the bags of greasy food and the drinks tray to the father, who passed them across to his wife and then drove away.

He had the patience of a saint, but he was fed up now. He had other things to do today; he didn’t want to waste a full day following them around. Hopefully now they had their food they’d go straight home and not park up somewhere to tuck into it. He pulled out onto the road a couple of cars behind them and trailed them as they drove onto the promenade, turning left and heading along the stretch of coastal road that led to a housing estate. He held his breath, hoping they wouldn’t indicate to drive into it, because it would be too busy. But the car drove past the estate and he paused to let a bus pull out in front of him; the roads were pretty quiet and he didn’t want them to realise they were being followed. Then again, why would they suspect any such thing? This was Brooklyn Bay, not London or Manchester.

Finally the car indicated to turn off. He couldn’t follow now because it wasn’t a busy street. There weren’t enough houses or cars for him to be able to blend in. In fact, there were only three houses that he could see, and all of them were detached with big gardens and hedges separating them. This was ideal – he couldn’t have chosen any better if he’d tried.

He had to know which house was theirs. He stopped his car on the street corner, took out his phone and put it to his ear, pretending to have a conversation whilst he watched as the Mercedes turned into the drive of the last house on the street. He waited to see how they entered the house; for all he knew they could just be visiting family. After five minutes he drove up the street – the front door was wide open and the kid was sitting on the front step eating his Happy Meal, still playing with his toy car. His mum stepped around him, opening the boot of the car and lifting out some of the shopping bags. Bingo.

Doing his best to look lost, he put his window down and asked her if she knew where Queen’s Drive was. She shook her head, which was fine by him because he didn’t even know if such a place existed. Turning the car around, he waved at the kid, who stared back at him. Then he drove off, smiling to himself.