Leave It to Psmith. by P. G. Wodehouse

Psmith, down on his luck, takes out a newspaper advertisement to undertake a job, and the Hon. Freddie Threepwood, younger son of Lord Emsworth, enlists Psmith to steal his Aunt Constance's diamond necklace. Psmith inveigles himself into Blandings Castle, posing as a Canadian poet. He falls in love with Eve Halliday and has to survive the suspicious and Efficient Baxter. In the meantime, others in Blandings Castle are also after the necklace.
Sir Pelham Grenville Wodehouse was an English author and one of the most widely read humorists of the twentieth century. After leaving school, he was employed by a bank but disliked the work and turned to writing in his spare time. His early novels were mostly school stories, but he later switched to comic fiction, creating several regular characters who became familiar to the public over the years.
Leave It to Psmith was originally serialized in the Saturday Evening Post in the U. S. and in Grand Magazine in the U. K. in 1923. It is the sequel to Psmith, Journalist.