Detective Inspector Marriot calls on Blunt's Brilliant Detectives and asks Tommy and Tuppence to hunt down a forger.

Somebody is passing forged notes at the exclusive Python Club in Upper Brook Street, and Detective Inspector Marriot feels that Tommy and Tuppence would be able to go under cover there better than any police officer. It is a very upper class establishment, and needs special attention.

Tommy and Tuppence agree with alacrity; Tommy invents the phrase 'the crackler' to describe a forger as they are going through their Edgar Wallace phase at Blunt's Brilliant Detectives and he believes that this word has the right feel to it. Alfred the office boy also assists in enquiries, going undercover as a motor cyclist.