The Sniffer Alley is infamous: a whole street full of detectives, and at its eastern end lives Hugo Abercrombie, the best detective in the world. While clients line up in front of Abercrombie's house every day, the other detectives suffer from a lack of cases. Uncle Gabriel is no exception, as the orphan boy Toby has recently moved in with him. One day, a letter arrives: the best detective in the world wants to retire and announces a competition to choose his successor. With the prize money, Uncle Gabriel's financial worries would be forgotten immediately, but he refuses to accept his rival's invitation. Secretly, Toby signs up himself. However, as soon as the detectives gather for the competition at Coleford Manor, the first dead body is discovered: Hugo Abercrombie himself.