A Town Called Mercy airs at 7.35pm on Saturday 15th September on BBC One and sees the Doctor find 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.

Watch the trailers…

> Order Series 7 Part 1 on DVD on Amazon.

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