Owen's manipulation of the Rift has perverted time across the globe, and both past and future are impinging upon the present. Bubonic plague threatens Cardiff, mighty spaceships hang in the sky, and the dead come back to haunt the Torchwood team. Gwen realises that the enigmatic Bilis Manger is the key to these events -- but is he a friend or an enemy? And what sort of being dwells in the darkness beyond the Rift?

From the beginning of development on the first Torchwood season, executive producer Russell T Davies knew that the opening of the Rift would feature prominently in the year's final episode. It was left to head writer Chris Chibnall to flesh this foundation out into a full script, originally known as End Of Days and then “Apocalypse” before it reverted to its original title.

Initially, Rhys did not survive the episode. Subsequently, however, Davies asked that this element be changed -- a modification Chibnall was happy to make he'd developed a fondness for the character. Chibnall originally envisaged Gwen taking Rhys to a hotel in her attempt to save him (with Rhys later returning to their apartment because he had forgotten to bring a change of underwear, whereupon he was stabbed by Bilis). Davies and executive producer Julie Gardner suggested simplifying the narrative by simply having Gwen bring Rhys to the Hub.

End Of Days was also responsible for writing Jack back into Doctor Who, for his appearances there late in its 2007 season. The episode was filmed together with Captain Jack Harkness by director Ashley Way. Its broadcast on New Year's Day 2007 brought the first season Torchwood to a close.

• Forthcoming.