Torchwood follows secret agents battling human and alien enemies
The new series of sci-fi show Torchwood will follow a single adventure instead of individual storylines, the BBC says.
Torchwood: Children Of Earth sees the team battling for the future of the human race against the fiercest force they have encountered.
"This series is one big serial and the most ambitious story we've ever made," writer Russell T Davies said.
Filming for the five-part series, which is due to be broadcast in 2009, has already begun in Cardiff.
John Barrowman will star as Captain Jack Harkness with Eve Myles - as Gwen Cooper - and Gareth David-Lloyd - as Ianto Jones - also returning in the third series of the Doctor Who spin-off.
"The new series of Torchwood is hugely bold and promises to be bigger and better than ever - the audience is in for an amazing ride," Davies said.
Julie Gardner, head of drama for BBC Wales, said: "We hope to make Torchwood a gripping and surprising TV event with storylines that push our team into greater danger and sacrifice."
The second series of the hit drama, which has been sold to more than 20 countries, attracted audiences of about 3.4 million when it was broadcast on BBC Two earlier this year.