THE DOCTOR AND DONNA NOBLE GATECRASH a party at Eddison Hall in 1926. The party is hosted by Lady Clemency Eddison, wife of the wheelchair user Colonel Hugh Curbishley. During cocktails on the lawn, the travellers meet the household and party guests: Clemency’s son Roger, socialite Robina Redmond, local vicar Reverend Arnold Golightly, butler Greeves, housekeeper Miss Chandrakala and footman Davenport. They are all surprised and delighted by the arrival of Clemency’s special guest, the mystery writer Agatha Christie, who has just discovered that her husband is having an affair.
A murder is announced as Miss Chandrakala discovers the body of Professor Gerald Peach in the library. He has been clubbed to death with a length of lead piping; the only clues are droplets of morphic residue and a burnt fragment of paper bearing the word ‘maiden’. Realising that the murderer is an alien, the Doctor introduces himself as Chief Inspector Smith of Scotland Yard and initiates an investigation with Donna and Agatha as his partners in crime. None of the suspects have an alibi, except for Roger and Davenport who are secret lovers and were together at the time of the murder.