The story is based on the ancient Greek tragedy Iphigenia at Aulis by Euripides. In the myth, Agamemnon, leader of the Greek army against Troy, accidentally kills a deer in one of Artemis's sacred fields. He is told by a seer that he must kill his eldest daughter, Iphigenia, in exchange, and his commanders pressure him into sacrificing her. In some tellings, she is killed; in others, she is transported elsewhere, replaced at the last moment with a deer/goat by Artemis. Some versions have her deified by Artemis after being transported.
The film follows a cardiac surgeon (Farrell) who secretly befriends a teenage boy (Keoghan) with a connection to his past. He introduces the boy to his family, who begin to fall mysteriously ill.
