When Lena Hartwell discovers an unfamiliar guest network inside her home router, she assumes it is a glitch. Then a hidden camera is found inside the kitchen vent, the nursery monitor activates from a sealed box, and an anonymous image arrives showing her inside her own house.

Her daughter has been dead for eighteen months. The nursery has remained untouched. But something inside the house has been watching Lena's grief, learning her routines, and using her most private pain as data.

As Detective Maya Sterling begins tracing the surveillance architecture, Lena realizes the intrusion is not the work of a simple stalker. It is a system: commercial, adaptive, and already embedded in the walls around her.

And the more Lena investigates, the more one question becomes impossible to avoid.

How much did her husband know?

Threshold is a dark psychological techno-thriller about domestic surveillance, grief, trust, and the terrifying moment when a home stops feeling like shelter.