The Secret Adversary !

The Secret Adversary is a work of detective fiction by Agatha Christie and first published in the UK by The Bodley Head in January 1922 and in the US by Dodd, Mead and Company later in that same year. The UK edition retailed at seven shillings and sixpence (7/6)、 and the US edition at $1.75. The book introduces the characters of Tommy and Tuppence who feature in three other Christie books and one collection of short stories written throughout her writing career.
Set in 1919, young couple Tommy Beresford and Tuppence Cowley form a partnership, hiring themselves out as "young adventurers". Their first case, however, is more of an adventure than they expect - working to find documents that, if they were known to the general public, would fuel a communist revolution in Britain.