Getting Happy with Parker Pyne: The Oracle at Delphi by Agatha Christie

Do it, Rockapella: Well he glides around the globe from Paris to
Damascus. He’s a double-dealing sleuth with a taste for trickery
He’ll take you for a ride on a slow boat down the Nile Tell me
where in the world is… Parker Pyne, heart specialist? This week
he's in Greece, in close proximity to an oracle, no less. You know
what that means: a kidnapping, an impersonation, and an attempted
jewel heist, of course. Enjoy!