The Secret of Chimneys by Agatha Christie
A young drifter finds more than he bargained for when he agrees to deliver a parcel to an English country house. Little did Anthony Cade suspect that a simple errand on behalf of a friend would make him the centerpiece of a murderous international conspiracy. Someone would stop at nothing to prevent the monarchy from being restored in faraway Herzoslovakia.
The combined forces of Scotland Yard and the French Surete can do no better than go in circles – until the final murder at Chimneys, the great country estate that yields an amazing secret.