The TARDIS arrives in Tombstone, Arizona in 1891. Where the Doctor is looking for a dentist when he has a toothache, where The Doctor finds the local dentist is the famous Doc Holliday who is in a feud with The Clanton Brothers and their hired gunfighter Johnny Ringo, whilst local sheriff Wyatt Earp is trying to keep the peace. The Doctor, Steven and Dodo find themselves joining forces with The Clanton Brothers and Sheriff Wyatt Earp.

With the Clantons believing the Doctor to be Doc Holliday, Wyatt Earp takes him into protective custody but this leaves Steven and Dodo in danger.

Earp comes to Steven's rescue and arrests Phineas Clanton, prompting the Clantons to decide to enlist the help of Johnny Ringo.