Getting Happy with Parker Pyne: Have You Got Everything You Want? by Agatha Christie

All aboard the... Orient Express?! That's right: heart specialist
Parker Pyne is going abroad, and while we've already covered one of
his travels in Christie's *other* Death on the Nile, here he
untangles a jewel heist (or is it?) aboard that infamous train
right around the same time Monsieur Poirot was taking it in the
opposite direction. (Maybe one day someone will find an alternate
And Then There Were None in the basement at Greenway, in which Pyne
finds himself on an island being hunted down by a murderer, only to
solve the murderer's problems by means of an elaborate theatrical
ruse....)