"Deep Breath" is the first episode of the eighth series of the British science fiction television programme Doctor Who, first broadcast on BBC One and released in cinemas on 23 August 2014.

In the episode, the newly regenerated Twelfth Doctor (Peter Capaldi), and Clara (Jenna Coleman) land in Victorian London where they find a dinosaur rampant in the Thames and a spate of deadly spontaneous combustions.

The episode has the first full-length appearance of Peter Capaldi as the Doctor, with Coleman reprising her role as his companion Clara from the last series.

[1] It also features Neve McIntosh, Catrin Stewart, and Dan Starkey reprising their roles as Madame Vastra, Jenny Flint, and Strax,[2] as well as Capaldi's predecessor, Matt Smith, in a cameo appearance.

Deep Breath was watched by 9.17 million viewers, the highest ratings for a premiere since Matt Smith's first episode as the Doctor in 2010 and received positive reviews, with many critics praising the performances of Capaldi and Coleman, Moffat's script, and the introduction and stylisation of the new Doctor, though Smith's cameo received mixed reviews.

Upon Clara's prompting, the awakened Half-Face Man reveals that he is trying to reach the "promised land" by prolonging his life via parts replacements and he killed the dinosaur to use her biological material for his computer.

[16][17] Brian Miller, who plays the tramp Barney, is the widower of Elisabeth Sladen who portrayed long-time companion Sarah Jane Smith.

[20] Steven Moffat, speaking at the London Film and Comic Con, called the leak "horrible, miserable and upsetting".

[31] Upon airing in its 7.50pm timeslot, the "Deep Breath" simulcast entertained an average audience of 6.79 million in the United Kingdom.

[33] This was also the highest final viewing figures for a regular series episode of Doctor Who since Matt Smith's first full episode, "The Eleventh Hour", was broadcast in April 2010, although Christmas specials and the 2013 50th anniversary special "The Day of the Doctor" had scored higher viewing figures.

[41] The episode received positive reviews, with many critics praising the performances of Capaldi and Coleman, Moffat's script, and the introduction and stylisation of the new Doctor.

Hogan notes that "the tone seemed different, too, quieter and more thoughtful – less about running down corridors holding hands, more about self-discovery and redemption."

Hogan also stated that the script was similar to Sherlock, for which Moffat also wrote, and was a bit slow in places, but still combined behind-the-sofa action with humorous comments about ITV and the Scottish Referendum.

[50] Brian Lowry of Variety praised Moffat's script, stating that it "emphasizes storyline continuity and easing faithful viewers into the regeneration transition" and closed his review by saying "It’s a skillful tonal balance that defines the best of “Doctor Who,” and exemplifies the ethos that keeps the series going strong, nodding to the past with all eyes on the future".

[59] David Wiegand of the San Francisco Chronicle heavily praised the episode, particularly Moffat's writing, saying that his script "masterfully manipulates audience expectation".

Forbes panned the story as "strangely recessive, unheroic, [and] dull", calling both Capaldi and Coleman's characters "insipid".

[61] The scene in which Madame Vastra and Jenny Flint exchange a kiss generated six complaints to Ofcom, with viewers criticising the BBC for promoting a "blatant gay agenda".