The Doctor, while attempting to correct the TARDIS's faulty navigation circuits, causes a small explosion. The Doctor, Barbara, Ian and Susan are all temporarily rendered unconscious. After they awake, Ian and Susan appear to have slight cases of amnesia and everyone begins to act strangely. Unexpected events are happening in the TARDIS, the travellers are becoming suspicious of each other's motives, and the Doctor even accuses Ian and Barbara of sabotage. Fearing that they have been taken over by some alien force—or that they have intentionally sabotaged the TARDIS in order to force the Doctor to return them to 1963—he drugs Barbara and Ian unknowing that Ian is also suspicious and has not taken the drink given to him. The Doctor attempts to explore the problem without interference.