After a crew member is found dead on board the nuclear submarine HMS Vigil, Detective Amy Silva is assigned to investigate the incident.
With the submarine *Vigil* in jeopardy, Amy must fight to keep her investigation alive. Meanwhile, Kirsten’s inquiries take a devastating and unexpected turn.
Kirsten's investigations take a new turn, uncovering a dangerous secret naval operation, prompting Amy to wonder who she can trust on board the submarine.
Kirsten gets closer to uncovering the killer's identity, and over time, more threats to the Vigil appear. Inside, Amy discovers a terrifying secret that changes the course of the investigation.
The submarine Vigil experiences an emergency that forces it to shut down completely. With communication cut off, Kirsten races against time to find evidence that reveals the source of the threat to the submarine and its crew.
Amy is trapped inside the submarine as time runs out. The Vigil crew seeks to identify the traitor among them before another catastrophe threatens everyone.