The body of young Froggy Quale lies, covered by a blue tarp, in the pasture behind Castle Dunlaggan in the Scottish Highlands.  Froggy was the on-site pollen and spore expert at the nearby archaeological dig and a graduate student who doesn’t seem to have had an enemy in the world. 

Dotsy Lamb, ancient and medieval history teacher from Virginia, and her friend, Lettie, are boarding at the castle while Dotsy works at the dig and Lettie researches her Scottish ancestors.  They and the other guests are cared for in the ancient castle by its owners, William and Maisie Sinclair. William’s archaeologist brother, Dr. John Sinclair, directs the dig.

Suspicion for Froggy’s murder falls on his roommate, Van Nguyen, a graduate student from America and the dig’s media man.  Dotsy has become fond of both Froggy and Van and is sure Van can’t be the killer. 

When John Sinclair also dies, the victim, Dotsy believes, of mushroom poisoning, his death appears to be either natural or accidental. But is it connected to the hallucinatory mushroom party at the camp site next to the dig?  Is the ownership of castle lands in jeopardy?  From whom?  What does an amethyst earring found in a pasture have to do with it, and how does Macbeth, the 11th century Scottish king, help Dotsy solve the mystery before the killer snares her in his trap?