The Doctor and Victoria adjust the Martian sonic cannon so it will only harm the Ice Warriors. Penley alters the temperature and atmosphere controls in the base so it becomes uncomfortable for the Martians. The Doctor fires the sonic cannon, forcing Varga and his men to retreat from the base. He fuses the sonic cannon before he and Victoria flee the ship. The Doctor works with Penley to recalibrate the Ioniser. The computer calculates a fifty-percent chance that the Ioniser will explode when trained on a spacecraft with an ion engine; Penley tells Clent to work without the advice of the computer. When the computer overloads, Penley takes charge and starts the Ioniser.