During the Balkan War of 1912, General Pherides (Boris Karloff) travels to a small Grecian island to visit the grave of his late wife. American journalist, Oliver Davis (Marc Cramer), accompanies him. Upon arriving, they find the coffin has been looted by thieves. Seeking shelter, they take lodging with Albrecht (Jason Robards Sr.), an antique collector. However, they soon discover the island is plagued by a deadly outbreak of the plague. As they struggle to survive, they begin to suspect that Thea (Ellen Drew), a young Greek girl, may be responsible for the deaths due to her being a vampire. As tensions rise and more members of the household succumb to the disease, Kyra (Helene Thimig), becomes increasingly superstitious and convinced of Thea's guilt. Eventually, the General becomes unhinged by the plague and Kyra's beliefs and tries to kill Thea, but is stopped and killed by a member of the household who had been in a cataleptic state and was mistakenly thought to be dead. Thea ultimately falls to her death from a steep cliff.