Paging the Doctor! When Martha gave the Doctor her old phone, this is the kind of situation she had in mind. Since he left, remarkable strides have been made in environmental engineering: in particular Atmos, a gizmo that is installed in half the cars on Earth which neutralizes exhaust, with only the tiny side detail of being completely evil and a front for alien murders. Atmos is the creation of a teenage genius named Luke Rattigan, who is secretly working for the Sontarans, a warrior race of militaristic short guys who look a bit like potatoes. (Though the Doctor would like to remind you that to a Sontaran, you look like a shaved pink weasel-thing.)