Martin is called to Louisa's new home after she has a dizzy spell while shifting furniture. Martin urges her to slow down, but is shocked to learn that Louisa has applied to be her school's head teacher again. Aunt Joan is involved in a car crash with the McLynns, an elegant elderly couple. When P.C. Penhale rushes to the scene and tries to impose his authority, he is ignored by both drivers. Edith visits Martin for some advice on her medical research, and Martin reveals he has applied for the prestigious surgeon's job in London. Wanting to confront Martin about his attitude towards her and the head teacher position, Louisa arrives on the seen and is taken aback to find Edith already there. Martin sees Mr. and Mrs. McLynn behaving oddly in the village, and makes an astonishing diagnosis.