Torchwood is the Doctor Who spin-off starring Captain Jack, who we first met in the Dr Who episode set in WW2 where Billie Piper was dangling from a Barrage Balloon.

The idea behind the series is similar to the Men in Black films, tracking down aliens and alien artifacts, but without much of the silliness of the films. Although it's not a comedy it also doesn't take itself too seriously.

It seems a strange decision to have the programme set in Cardiff but then again it makes a nice change from having everything set in London (it was explained in the first episode that they had been several 'Torchwood' groups around the country). More 'grown up' than Dr Who (read: has sex in it) which accounts for it being on later.