Detective Inspector Peter Carlisle moves into 221B Baker Street, in the spare flat by Sherlock Holmes and Doctor John Watson. At first, he and Sherlock conflict, before discovering that they have, in fact, things in common, such as their deductive skills. Soon, they work together to begin unravelling a series of serial killers and various crimes, whilst building up a companionship of sorts. Mycroft is not particularly happy, as he believes that Peter is a bad influence, while Moriarty enjoys taunting the two detectives.