On a lazy June afternoon in 1925 the TARDIS materialises at the tiny railway station of Cranleigh Halt. Warmly welcomed by the local gentry, the Fifth Doctor, together with Tegan, Adric and Nyssa, is invited to the splendid masked ball by Lady Cranleigh and her son, Charles.
But a dark menace haunts the secret corridors of Cranleigh Hall. And before the ball is over, the quiet summer will be shattered by the shocking discovery of a brutal murder.