You had to accept that nothing might come of it, that you could be wasting your time. You had to avoid visualising what you hoped to witness, or even wondering what would constitute an act or sight worth witnessing. You just had to wait and see, wait and see.

Of course, this was made a little more challenging by the fact that Catherine was engaged in an unauthorised surveillance of a fellow officer, and that there was a limit to how much time she could dedicate to such a one-woman operation, but that again was something she’d had to make her peace with before commencing. She accepted she might see nothing, and just as important, she accepted that there might be nothing to see.

At the moment, though, she was optimistic that she was finally on to something. When you’ve been watching someone drive all day, you can notice small tells, subtle changes to how they are handling their vehicle. In the case of Abercorn right then, it was similar to someone driving over the alcohol limit: he seemed just that bit more careful and deliberate about everything. Or maybe it was simply that, after a day largely spent around the city centre, he was finally heading into Apache territory.

He drove east along the Gallowgate, past the Barrowland and round the dog-leg up to Tollcross Road. His pace was steady and careful, keeping his distance from the car in front. He couldn’t have made himself much easier to tail. There were no evasive manoeuvres, no doubling back on himself or sudden non-indicated turns. Only his route was questionable, and only in retrospect. He turned left off Tollcross Road before it became Hamilton Road, heading north past Tollcross Park and east again on to Shettleston Road, only to come back south through Mount Vernon and end up travelling east again on Hamilton Road. Could be he knew about a traffic issue, could be he changed his mind about his route, but Catherine was aware that if he had any suspicions about the black BMW two and sometimes three cars back, then an unnecessary U-shaped detour would be a good way to confirm them.

He’d need to have spotted her way back, however, and that didn’t strike her as probable. She had kept a minimum one-vehicle cover, and with him never getting an eyeball on her face or her plate, if he even noticed that there was a black BMW somewhere behind him, it was unlikely he’d assume it was the same one.