The novel features Ogden Ford and his mother Nesta, both previously encountered in The Little Nugget (1913).

Nesta has remarried the diffident, baseball-loving millionaire Mr Peter Pett, and Ogden remains spoilt and obnoxious.

The story takes its title from the charismatic character of James "Jimmy" Crocker, Nesta's nephew and a reforming playboy.

'Jim' is called upon to assist in the kidnapping of Ogden, amongst much confusion involving imposters, crooks, detectives, butlers, aunts etc.

Financier Peter Pett lives in a New York mansion with his formidable wife, crime novelist Nesta Ford Pett, his step-son, the stout and ill-behaved fourteen-year-old Ogden Ford, and his niece, the strong-willed Ann Chester.

Mr Pett sees an article in the New York Sunday Chronicle about Mrs Pett's 21-year-old nephew, James Braithwaite Crocker, a wild young man called "Piccadilly Jim" who is currently in London but used to work for the Chronicle.

Mrs Pett decides the family will go to London to bring Jimmy back and keep him under control in New York.

Ann suggests to Jerry that they kidnap Ogden and send him to the pet hospital run by Mitchell's friend Smithers, who cures sick dogs with a regimen of a healthy diet and exercise.

Lord Wisbeach warns Mrs Pett to safeguard the explosive powder called Partridgite invented by her nephew Willie Partridge.

He plays along with his father being the butler, and also pretends to recognize Lord Wisbeach, though he realizes the man is an imposter.

[3] The UK edition was the first novel written by Wodehouse to be published by Herbert Jenkins.