The Secret Adversary - Agatha Christie (HarperCollins)

The Secret Adversary [Masterpiece edition] - Agatha Christie.
Published by HarperCollins in 2007. Originally published by John Lane in 1922.

From harpercollins.co.uk:
2007, Facsimile of 1922 UK first edition (HarperCollins), November 5, 2007, Hardcover, 320 pp ISBN 0-00-726515-8
Agatha Christie’s first Tommy and Tuppence mystery adventure, reissued with a striking new cover designed to appeal to the latest generation of Agatha Christie fans and book lovers.
Tommy and Tuppence, two young people short of money and restless for excitement, embark on a daring business scheme – Young Adventurers Ltd.
Their advertisement says they are ‘willing to do anything, go anywhere’. But their first assignment, for the sinister Mr Whittington, plunges them into more danger than they ever imagined…