A Jack themed episode

Whilst investigating an old, derelict dance hall, Jack and Tosh are transported back to the 1940s, during the Blitz. Owen, Ianto, and Gwen realise, in modern day, that this has happened, and go in search of clues Tosh may have left. Meanwhile, back in the forties, Jack meets a very interesting man. One with the name Captain Jack Harkness...