Paige almost echoed the sound as she saw the win, because in that moment, she thought that she understood. She turned and ran back towards her home, darting back across the street, oblivious to a car whose horn blared as it only barely missed her. She had to get back before the shape of this idea fled from her. She had to see the timeline again to be sure.

Paige ran up the stairs to her apartment, kind of grateful now for the improved fitness that the FBI’s training program had started to give her. She reached the door to her apartment, let herself in, and ran over to her refrigerator.

The timeline was still there, but now, Paige could see the pattern in it, the one that she’d been missing. It wasn’t about any kind of regular interval between kills but was instead all about the grouping of kills.

In every case after the Nikki Ashenko murder, one kill was closely followed by a second, usually just a few days after it. There were a couple of spots where that led to a third and fourth kill, too, as if the two had been going back and forth, bouncing murders between them like some deadly game of tennis.

It was call and response. One, Paige guessed Lars Ingram, would kill, and then the other would manage a kill of his own. Paige looked at the files for the murders, and she saw something else, too: the second murders were always at least as difficult as the first. Where Ingram took an easy kill in an almost empty house, so did the second killer. Yet on an occasion where Ingram had killed an au pair while her entire host family was home, the next kill had been a nurse working overnight in a clinic, where there was very little chance of controlling the surrounding environment.

This killer didn’t just want to copy Ingram; he wanted to beat him.

Paige felt as though she could start to divide up the board now, with the first of any pair going to Ingram, the second to the copycat. It meant that, in the period when both had been active, they’d killed the same number of people, but Ingram had always had that nagging head start of those three original kills.

So in the days leading up to Ingram’s execution, the killer had deliberately made three kills of his own, wanting to level the tally before his rival, his competitor, died.

That wouldn’t be enough, though, would it? Being level with Ingram wasn’t going to satisfy this killer. If Paige understood what was happening, then he wasn’t going to settle for just tying this game with Ingram. He was going to want to win it, maybe to take over as the undisputed champion of their deadly, sick game. He was going to want to make one more kill.

It had to be today, didn’t it? That part seemed almost obvious now that Paige thought about it. The one-upping of Ingram’s kills said to her that this killer cared about the way things were done, as well as the numbers. He wouldn’t let the day of Ingram’s death go unmarked.

It wouldn’t just be any kill, either. For the one that let him win, the killer wouldn’t want some run of the mill, easy victory. He would want something that represented a challenge, something that was meaningful. Now, Paige just had to work out what, and she needed to work it out now. With the killer still out there, there was no time left.