For readers of CJ Tudor and Jane Harper comes a heart-stopping new thriller from the bestselling author of The Memory Wood and The Rising Tide.

I watch them because I think they need help.

Mercy Lake likes to fix things. To fix people. Trapped inside during daylight hours, hostage to her phobias, she uses the cover of night to watch the people in her town. And if someone needs her help, she steps in—secretly and with compassion.

When Mercy meets Louis, her lonely, unusual life is suddenly filled with excitement. Because Louis likes intervening in other people's lives too, only he prefers a more direct—even violent—approach. As they grow closer, Mercy is enchanted but frightened by his actions. How many lines is he willing to cross? And how much is he prepared to risk?

And then there's Nadia. Nadia knows she's being watched, even if the police think differently. But with her own secrets to protect, she's not going to wait around for the watcher to make their move. She's going to stop them dead.