Partners in Crime by Agatha Christie

Tommy and Tuppence Beresford are restless for adventure, so when they are asked to take over Blunt's International Detective Agency, they leap at the chance.

Their first case is a success—the triumphant recovery of a pink pearl. Other cases soon follow—a stabbing on Sunningdale golf course; cryptic messages in the personal columns of newspapers; and even a box of poisoned chocolates. But can they live up to their slogan of "Any case solved in 24 hours"?