"The Hounds of Baskerville" is the second episode of the second series of the BBC crime drama series Sherlock, which follows the modern-day adventures of Sherlock Holmes, and was first broadcast by BBC One on 8 January 2012. It was written by co-creator Mark Gatiss, who also portrays Mycroft Holmes, Sherlock's brother in the series, and was directed by Paul McGuigan. The episode is a contemporary adaptation of The Hound of the Baskervilles, one of Sir Arthur Conan Doyle's most famous works. In the episode, Sherlock (Benedict Cumberbatch) and his crime-solving partner John Watson (Martin Freeman) take on the case of Henry Knight (Russell Tovey), who 20 years earlier witnessed the brutal killing of his father by a "gigantic hound" on Dartmoor. The investigation leads the pair to Baskerville, a military research base. In the conclusion it is revealed that the hounds were images induced by a mind-altering drug, a chemical weapon whose creator was in fact the real murderer of Henry's father. Because of the popularity of the novel, Gatiss felt a greater responsibility to include familiar elements of the story than he did when adapting the lesser-known stories. The script was intended to follow elements of the horror genre and make the episode scary. As opposed to traditional ghost stories, Gatiss's plot focused on more contemporary horrors, conspiracy theories and genetic modification. Filming was done throughout May 2011, with additional shots taking place as late as August. Location shooting took place mostly across South Wales, though parts were shot in Dartmoor. The hound was created using visual effects. After its broadcast on BBC One, the episode received consolidated figures of 10.266 million viewers in the United Kingdom. This rating, although a slight drop from the previous episode, still represented the second largest audience in British television the week it aired. Critical reaction toward the episode was largely positive, with reviewers praising both the modernisation and its tonal fidelity to the original. Critics praised Cumberbatch, Freeman, and Tovey, as well as Sherlock's "mind palace" sequence.