A 7 year old is looking for his mother in London in World War 2. He gets damaged by something and then nanobots from an ambulance machine which Captain Jack Harkness tried to sell and crashed healed him, he was wearing a gas mask and so the nanobots thought that that was what humans looked like so they bonded it to his face, now he terrorised people asking, "Are you my mummy?" When anyone touched him they would turn into him get a gas mask attached to their faces and made them repeat, "Muuuuuummmy, are you my mummy?" His 'sister' turned out to be his mum, she was a teenage mum. He touches her then the nanobots realise they made a mistake then hey presto "Everyone lives", like the 9th Docctor says.