Mary Yellan arrives in Cornwall to live with her Aunt Patience at the remote Jamaica Inn after her father’s death. She quickly realises the inn is controlled by the violent Joss Merlyn and suspects criminal wrecking and smuggling are practiced there. Mary meets Joss’s charismatic younger brother Jem and the reclusive vicar Francis Davey while trying to protect her aunt.

Mary digs deeper into the inn’s illicit activities as evidence mounts of murder and wrecking. Conflicts within the Merlyn family intensify; Jem’s ambiguous loyalties are revealed and Mary faces increasing threats. She seeks help from Reverend Davey while tension and violence escalate around the inn.

The criminal operation at Jamaica Inn unravels: betrayals come to light, confrontations turn violent, and Mary must act to save herself and Patience. The fates of Joss, Jem, and Reverend Davey are resolved as the series reaches its dramatic conclusion.