The Boscombe Valley Mystery (The Adventures of Sherlock Holmes, Episode 4)

Inspector Lestrade asks for Holmes's help after Charles McCarthy is murdered, and his son, James, is implicated. McCarthy, and another local landowner, John Turner, are both Australian expatriates, and Lestrade was originally engaged by Turner's daughter, Alice, who believes James is innocent. Holmes interviews James, and then inspects the scene of the murder, deducing a third man was present. Realising Holmes has solved the case, Turner confesses to the crime, revealing that McCarthy was blackmailing him due to Turner's criminal past. Holmes does not reveal the crime, but secures James's release because of the presence of a third person at the crime scene.