WPC Gwen Cooper is at the scene of a brutal murder, when the "special ops," known only as Torchwood, arrive. After witnessing the group bring the dead man back to life, Gwen goes in pursuit of this mysterious organisation, only to see weirder things than she could ever imagine existed. Soon after, she begins to regret giving in to her curiosity, when she meets Captain Jack Harkness.

It's Gwen's first day on the job, and it's not going very well. After accidentally releasing a mysterious gas from a comet that landed, a new type of alien is let loose on the streets - an alien that's addicted to sex. Torchwood must find the inhabited body, and prevent anymore deaths from the violent form of sex.