Agatha Christie 
Rajah’s Emerald [EPUB ebook] 

James has found himself at the fashionable resort Kimpton-on-Sea, all due to the persuasion of his girlfriend Grace, who during the last few months of their courtship has become more difficult to deal with. Among the upper echelons of society, including the Rajah of Maraputna, James feels disgruntled and out of place. Eager to both irritate and win over Grace, James bypasses the queue to the changing rooms and ducks into the private huts on the beach so that he can be the first into the sea. It is only later that he realizes he has accidentally come into possession of a very valuable and sought-after object.