The Red Headed League was a villainous criminal faction in the No Place Like Holmes Series. It dealt in art and antiquities stolen to order, but ventured into near enough anything profitable. It was headed up by Madeline Chambers. The group's name derives from the Sherlock Holmes story "The Red Headed League" by Sir Arthur Conan Doyle.
It first became apparent such a group existed at the end of the episode "Red Rising", when Holmes foiled one of their members plans to steal a handbag. The 3rd and 4th series saw the RHL's focus on crime lessening, choosing instead to try and find the truth behind Sherlock Holmes hidden past and how best they could exploit it.
Originally the group consisted of Madeline Chambers and Braderick Theobald, with the intent being for Rebecca Constance to join as the 3rd member, but due to Braderick's actor (Barnaby Twyman) leaving the show, the decision was made to promote Rebecca, and the RHL effectively became a two-woman operation.
The RHL ceased to exist as a cohesive unit in between the 5th series episodes "The Sign Of Things To Come" and "Truth Or Date" in which we learn that Rebecca has been arrested and jailed for tax evasion. Not caring enough to do anything to help her friend get out of jail, much like it's original incarnation in the original ACD tale, the League effectively disbands.