Ex-soldier Lee Arnold and his Muslim assistant Mumtaz Hakim run a detective agency in London's ethnically diverse, crime-ridden East End.

Mumtaz is approached by an Egyptian woman, Salwa, whose husband is in Belmarsh prison on terrorism charges.

Salwa convinces Mumtaz of her husband's innocence and persuades her to go undercover to prove it. But Salwa is not what she seems.

Trapped in an old tunnel that leads to the London docks, will Mumtaz escape with her life?