The BBC series Sherlock episode featuring Charles Augustus Magnussen is “His Last Vow.” It is the third and final episode of series 3 and first aired on BBC One on 12 January 2014.
Magnussen, played by Lars Mikkelsen, is a powerful newspaper magnate who collects compromising information about influential people. Sherlock and John become involved in a case centered on Magnussen after Mary Watson’s concealed past is exposed and John is placed in danger.
The episode adapts ideas from “The Adventure of Charles Augustus Milverton,” a Conan Doyle story about a blackmailer. Sherlock changes the setting and details but preserves the central concept of an antagonist whose power comes from private information rather than physical force.
“His Last Vow” is also notable for its final confrontation at Appledore, Magnussen’s estate, and for its closing cliffhanger involving Moriarty. It is sometimes confused with “The Reichenbach Fall,” which centers on Moriarty’s earlier major conflict with Sherlock.