You’re trapped underground. There’s no way out. And there’s a killer on the loose…

When former Detective Inspector Jess boards the London Underground, it should be just a few short stops home. But as the tube barrels towards Baker Street, it’s brought to an abrupt stop, and they’re plunged into the darkness.

And then she hears the screeching.

Jess pushes through into the driver’s cabin. There, she finds his lifeless body, and stab wounds in his neck, still bleeding. But if nobody could get into the cabin from the outside, and nobody else could get into Jess’s carriage, the realization strikes there's a murderer among the passengers.

With no escape from the train, and in the pitch black, Jess is thrust into a deadly game. Every commuter becomes a potential threat, and time is ticking on relentlessly. In a race against the unknown murderer, Jess must unravel the sinister truth before the killer strikes again…