In Castle in the Desert, Charlie Chan (Sidney Toler) visits sprawling Manderley Castle and crosses paths with a descendant of the Borgias, the medieval family famous for poisoning their enemies. The Borgias lived centuries ago, but the poisoned corpses that begin piling up in the castle are quite fresh, and Charlie soon realizes he's been summoned to witness these grisly murders! Determined to unmask the culprit, the master sleuth turns up the heat on the killer to unveil a complex scheme of lies and lethal deception!