Although the series depicts a variety of crimes and perpetrators, Holmes' conflict with archnemesis Jim Moriarty (Andrew Scott) is a recurring feature. Molly Hooper (Louise Brealey), a pathologist at St. Bart's Hospital occasionally assists Holmes in his cases. Other recurring roles include Una Stubbs as Mrs Hudson, Holmes and Watson's landlady, and series co-creator Mark Gatiss as Holmes' elder brother Mycroft.