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 time-travellers look forward to a well deserved rest from their adventures.

After a stunning performance at a friendly cricket match, the Doctor, together with Tegan, Adric, and Nyssa, is invited to a 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.