"The world doesn't end 'cos the Doctor dances."The Doctor, Rose and Jack desperately try to escape the gas mask people and figure out what the hell is going on. While Jack teleports away, Rose and the Doctor are trapped for a while, and Rose takes the opportunity to ask the Doctor if he can dance like Jack can. The Doctor is a bit offended, and says he's actually got quite an amount of experience with... dancing. Rose really can't picture him... dancing. While the Doctor steps closer and takes her hands for an intense... dance, they fail to look around and realize that Jack's already saved them. It also turns out that Jack isn't exactly with the Time Police any more; he turned rogue after waking up one morning and finding that two years of his memory had been wiped by his employer.Jack goes off to distract a gay crash site guard with his suave, omnisexual allure, and the Doctor explains to Rose that Jack is, quote, "just a bit more flexible when it comes to... dancing". In Jack's century, people will travel the whole universe to find aliens of all sexes and genders, and... dance with them. Meanwhile, the virus becomes airborne and everyone around the warship crash site starts mutating.Seeing the crash site, the Doctor figures it out: the Chula warship was a field ambulance,note and contained nanobots (here called "nanogenes") for expedient battlefield healing. When Jamie was first hit by the ship, the nanogenes swung into action and tried to fix him... but they'd never interacted with humans before, and so derived their idea of what humans looked like from a badly wounded kid in a gas mask. They sort of made it up as they went along — assuming that fully healed people wore gas masks, they made the people they "infected" sprout gas masks. But when they finally met Nancy (really Jamie's mother, not his sister), they had a different model of a healthy human being to work towards... and the parent/child relationship between the subjects meant that the nanogenes knew that this pattern was the right one.Everybody Lives as the Doctor re-infects everyone with the nanogenes, who now know how to fix humans. Even previously dead humans. Hooray! Also, Captain Jack joins the TARDIS, saved by the Doctor just before his ship goes kablooey in an attempted Heroic Sacrifice. He walks in to find the Doctor and Rose... dancing. Rose asks if Jack would like to cut in and also... dance. The Doctor, amused to have an openly not-straight companion, wonders which of the two Jack would... dance with.