“‘The Well-Worn Lock” is the eighth episode of the first season of the American crime-thriller television series Millennium. It premiered on the Fox network on December 20, 1996. The episode was written by series creator Chris Carter, and directed by Ralph Hemecker. “The Well-Worn Lock” featured guest appearances by Paul Dooley and Lenore Zann.

Clinical social worker Catherine Black aids a family as they come to terms with the incestuous abuse they have suffered for decades. However, the father who is responsible still commands respect and political connections in the area, making the case a difficult one.

“The Well-Worn Lock” is the third of seven Millennium episodes written by Carter. Hemecker would return to direct an episode in each of the show’s seasons. The episode opens with a quote from Robert Louis Stevenson, and features several actors who would reappear in unrelated roles in both Millennium and its sister series The X-Files.