After a run-in with an unkown piece of machinery, two of the Torchwood team find themselves temporarialy changed into their younger days. The rest of the team tries to find a way to help them change back with some outside help. ToshOwen JackIanto

The title basically says it all doesn't it? Well for the very dim minded I will explain. The Doctor and Donna land in Cardiff and meet the team of Torchwood. Multiple pairings. Completely ignores Stolen Earth, Journey's End, Fragments and Exit Wounds.