Using the TARDIS scanner, the Doctor locates the Terileptil in London. The TARDIS rematerialises there and the five enter the building. With the Terileptil leader are two others who get the jump on the Doctor and Mace. They manage to stop them, but the Terileptil leader's weapon starts to overload and detonates. The resulting explosion destroys the building and starts a raging fire. Mace stays behind to fight the blaze as the Doctor, Tegan, Nyssa and Adric leave in the TARDIS.