Getting Happy with Parker Pyne: The House at Shiraz by Agatha Christie

Bar the gates, because Parker Pyne is still abroad, flitting here, there, and everywhere in the Middle East. This time we find him in Persia (i.e., Iran)--specifically, the lovely city of Shiraz. But not so lovely as to prevent it from harboring one who is some combination of murderer, lunatic, and/or impostor. Let's sort it out together before our peripatetic PI jets off someplace else for further adventures.