Quarry Lake. Twelve years ago.

Three young women are attacked, all with long, dark hair. The attacker wears a yellow hi-vis jacket.

One is murdered.

One is left in a coma.

One escapes.

A small town lives in fear.

It's Riona's last summer before heading to university. One reckless night, she lets her two friends persuade her to spend the evening at Quarry Lake, drinking cider, sharing secrets, planning their futures.

They hear a scream and a splash. They're scared but they feel they have to go and see what it is. But a sudden noise frightens them, and they run off.

Now, Riona is back in her hometown, facing thirty with some of her dreams still intact.

They never did catch the Quarry Lake killer.

But one day Riona glimpses a mysterious figure in a hi-vis jacket. Staring intensely at her.

A note is shoved through her letterbox: I'm watching you.

Is the past coming back to threaten her? Is the killer back?