Alan Cox and Freddie Jones both appeared together previously in Young Sherlock Holmes (1985). The film also starred Nicholas Rowe, who appeared two episodes earlier in "The Fisher King."
Peter-Hugo Daly plays Wesley in this episode. He returns in episode 12.1, The Dogleg Murders (2009), in the role of Archie Kemp.
Elaine Donnelly plays Maureen Cruickshank in this episode. She previously played the role of Elaine in episode 4.1, Garden of Death (2000).
William Gaunt plays Michael Bannerman in this episode. He returns in episode 15.1, The Dark Rider (2012), in the role of Ludo DeQuetteville.
Sophie Hunter (Bella Monday) is married to Benjamin Cumberbatch (which is obvious if you look up her images on IMDb as they appear to be joined at the hip). The actress who played that character's mother, Frances Tomelty (Audrey Monday) was married to Sting from 1976-1984).