The Doctor, Rose and Captain Jack Harkness are still in the hospital with the gas mask-wearing mutants and are having some trouble finding a way out. The Doctor determines that the ambulance Captain Jack was using in his scam contained nano genes, similar to the one's he used to repair Rose's rope-burned hands. Only in this case, there are enough nano genes on the loose to "repair" an entire species and they have no idea what a human looks like in the first place. The future of the human race lies in Nancy accepting her true relationship to the little boy who is haunting her.