When a lost archaeological expedition discovers a mysterious burial urn, the young student who opens it suddenly collapses in convulsions. Though she quickly recovers, Professor Hamilton, the expedition's leader, suspects she's contracted a disease from the urn's skeletal remains. He believes that's the only rational explanation for the inscription on the urn, warning that an evil demon is imprisoned within.

But the next day, Roxton and Marguerite discover the expedition's camp has been torn apart, and that of all the archaeologists only two survive-Hamilton and his rival, Professor Campbell. In a tense standoff, the two men claim the other is possessed by the demon. Roxton's and Marguerite's intervention only succeeds in making the archaeologists suspect the demon has jumped into one of the two explorers.