London 1890. Inspector Tobias Gregson is an ambitious officer at Scotland Yard. However, his career is hindered both by his overly humanitarian and sensitive nature and by his superior, Lestrade, who often takes out his frustrations on him. When a prisoner transport goes awry, Gregson is held responsible and sidelined. This reprimand quickly turns into an opportunity for him to prove his true worth to the big boss, Commissioner Fix. Leading a rather unusual team made up of a street boy and former informants of Sherlock Holmes, a psychiatrist with peculiar methods, and his quirky assistant, Gregson is set to form an alliance with the devil: he intends to cooperate with the London underworld to hunt down two extremely dangerous lunatics responsible for the debacle.