 He and Donna return to the ATMOS factory, where the Doctor warns UNIT not to engage the Sontarans.The Doctor tells Donna to stay in the TARDIS for her own safety, but the Sontarans locate and teleport the TARDIS aboard their ship.When the Sontarans prevent UNIT from launching a nuclear missile at their ship with help from the clone of Martha, the Doctor works out that since their ship was safe, the Sontarans were really preventing the disruption of their atmospheric conversion.