Doctor Who will welcome back Mark Gatiss for season 9.

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The Sherlock actor and co-creator is currently penning an episode for the 2015 run of Doctor Who.

"I'm in the midst of that right now - I broke off to come here today, in fact, but I'm hoping to finish the script tonight," Gatiss told The Telegraph on Saturday. "It has been a tough nut to crack, but I'm delighted with how scary it is. I can't say any more than that."

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Gatiss previously wrote "Robot of Sherwood," "The Crimson Horror," "Cold War," "Night Terrors," "Victory of the Daleks," "The Idiot's Lantern," and "The Unquiet Dead."

It is currently unknown whether or not Gatiss' episode will feed into one of season 9's multiple two-parters. Considering it appears the scribe is only working on one episode, his inclusion in the new multi-part episode scheme seems unlikely.

Find out more when Doctor Who returns to the BBC and BBC America this fall. Click the video below to see a preview for Gatiss' season 8 episode, Robots of Sherwood.