Based on the novel by Michael Marshall Smith, "Intruders" is a paranormal thriller about a secret society who search for immortality by seeking refuge in the bodies of others. Jack Whelan (John Simm) finds the quiet, idyllic life he has created with his wife, Amy (Mira Sorvino) suddenly shattered when she vanishes. He's drawn deeper into the mystery when his high school friend, Gary Fischer, shows up on his doorstep asking for help with a murder case. Initially dismissive of Gary's claims, Jack finds that the further he investigates, the more complex and surreal his discoveries become. What he uncovers leads him down the dark path of his own past, and closer to terrifying revelations about a clandestine group known as Qui Reverti. Meanwhile, in order to conceal the truth, an assassin named Richard Shepherd is embarking on a series of executions, and is in pursuit of a seemingly innocent nine year old girl, Madison - a runaway with a score to settle who could be the end of them all. With Gary's help, Jack begins to discover the incredible truth about his wife and her connections with Qui Reverti, determined to find and save the woman he loves.