The TARDIS materializes in the town of Tombstone, Arizona, just in time for the Gunfight at the O.K. Corral. The Clanton Brothers are looking for Doc Holliday to kill him for the death of their brother Reuben. Kate (Sheena Marshe), a singer in the saloon, warns Doc Holliday.
The Doctor has a toothache and goes to the local dentist—Doc Holliday, played by Anthony Jacobs—while Dodo and Steven book rooms at the hotel. The Clantons overhear them speaking of The Doctor and believe they are friends of Holliday. Marshall Wyatt Earp (John Alderson) and Bat Masterson (Richard Beale) take The Doctor into custody to protect him. Then Johnny Ringo (Laurence Payne) shows up, also the rest of the Earp Brothers.
Later, when it becomes clear that The Doctor is not, in fact, Doc Holliday, the Doctor introduces himself as Doctor--um--Caligari, to which the answer is, “Doctor Who?” “Yes. Quite right.”
There are complications, escape attempts, lynching attempts, and shootings in Tombstone and at the Clanton Ranch. The Doctor attempts to defuse the situation, but the Gunfight takes place as it was meant to. The time-travellers leave in the TARDIS.
Sooner or later, every science-fiction series has a Western episode. This one came with an original song called “Ballad of the Last Chance Saloon.” But despite this, or because of it, the story was not a favourite. Nobody tried a Doctor Who song again until 2005.