John Whitney, an anthropologist for the Field Museum of Natural History in Chicago, studies a tribe in South America and drinks a soup made by the tribesmen. Shortly after, Whitney accosts a merchant ship captain, asking him to remove the cargo he had intended to send to Chicago off the ship. Unwilling to delay the ship's departure, the captain refuses and Whitney sneaks aboard. Not finding his cargo, he cries out. Six weeks later, the ship arrives on Lake Michigan with its crew missing. Chicago Police Department homicide detective Lieutenant Vincent D'Agosta and his partner, Sgt. Hollingsworth, investigate the ship and find dozens of bodies and severed heads in the bilge.