Doctor Who - Season 7 - Eps 3: A Town Called Mercy
The Doctor gets a Stetson (and a gun!), and finds himself the reluctant Sheriff of a Western town under siege by a relentless cyborg, who goes by the name of the Gunslinger. But who is he and what does he want? The answer seems to lie with the mysterious, Kahler-Jex, an alien doctor (yes another one!) whose initial appearance is hiding a dark secret.
About Doctor Who

Title: Doctor Who
First Air Date: 2005-03-26
Last Air Date: 2021-12-05
Status: Ended
Rating: 7.5/10 (from 3098 votes)
Language: EN
Seasons: 14
Total Episodes: 153
Network: BBC One
Genres: Action & Adventure, Drama, Sci-Fi & Fantasy
Production Companies: BBC Cymru Wales, BBC Studios, CBC
Synopsis
The Doctor is a Time Lord: a 900 year old alien with 2 hearts, part of a gifted civilization who mastered time travel. The Doctor saves planets for a living—more of a hobby actually, and the Doctor's very, very good at it.
Cast

Jodie Whittaker
The Doctor

Mandip Gill
Yasmin 'Yaz' Khan

John Bishop
Dan Lewis