Rosa recognised her from her photos and her heart quickened. The last time she’d seen Laura Jefferson had been two nights ago when she’d tried to kill her at her home in Balham.

Now the detective was striding purposefully towards where she stood. And the look in her eyes was one of grim determination.

Rosa was suddenly alert, but not unduly alarmed. This is nothing more than a wicked coincidence, she told herself. It can’t be anything else.

Nevertheless she went very still as Jefferson walked towards her through the crowd. She looked to be in a hurry and paid no attention to the flowers on the ground.

Rosa unzipped her bag, ready to grab the pistol inside if necessary.

‘Time to go, I think,’ Alice said, squeezing Rosa’s hand. ‘If I stay here any longer I’ll probably start crying.’

Rosa didn’t move because at that moment Jefferson walked past them. Their eyes locked for a fraction of a second, but in the detective’s there was no sign of recognition.

Rosa let out a breath she didn’t know she’d been holding, and then allowed Alice to lead her away from the forecourt and onto the pavement.

But Rosa’s eyes followed Laura Jefferson, who walked up to the edge of the kerb and flagged down a black taxi.

The chance encounter had lasted only a few seconds, but it took much longer for the tension to leave Rosa’s body.

What were the odds on that happening? she wondered. Ten million to one maybe. And what would she have done if the woman had recognised her? It was something that didn’t bear thinking about.

The detective was the first target that Rosa had missed, and for that reason the woman intrigued her. She made a mental note to find out more about her. Purely out of interest. She wondered how long she had been a police officer. Whether she had children. If she had ever killed anyone.

And for some reason that Rosa couldn’t explain she was glad that Laura Jefferson was still alive.

Perhaps it was because two nights ago she had proved to be such a worthy adversary.

The South Bank was throbbing with people, mostly tourists and groups of students. And there were quite a few uniformed cops. But unsurprisingly Rosa was in no position to take any of them out.

It wasn’t a problem, though, because she was prepared to bide her time. She was sure that sooner or later she would see an opportunity and be able to slip away from Alice. It wouldn’t take long or be that difficult to shoot an unsuspecting cop. She would just have to make sure that she wasn’t seen or caught on camera.