Set in 1820 against the forbidding backdrop of windswept Cornish moors, the story follows the journey of young and spirited Mary (Brown Findlay) who is forced to live with her Aunt Patience (Whalley) after the death of her mother. Mary arrives at the isolated Jamaica Inn to discover her Aunt is a shell of the carefree woman she remembers from her childhood, and instead finds a drudge who is firmly under the spell of her domineering husband Joss (Harris). The Inn has no guests - the rooms are locked and kept for storage - but it soon becomes clear that it’s a cover, as Joss is the leader of a smuggling ring, and Jamaica Inn the hub of his ‘free’ trade.
Mary moves in with her Aunt when her mother passes away, avoiding her marriage to local boy Ned. Her Aunt Patience has changed remarkably when Mary finally arrives, as her uncle Joss has battered her down from the woman she once used to be. Mary finds herself drawn to Joss' brother Jem Meryln but has been warned away from him before now.
Joss' night terrors lead to some dramatic confessions as Mary begins to settle in to life at the Inn. Mary confides in Francis Davey, the local vicar and his sister Hannah, when she learns of the sailors Joss has killed. Jem saves Mary later on when she finds herself in peril on the Moors.
Mary doesn't know who to trust as the net on her uncle and his smuggling tightens and Jem is taken into custody. Jem wants to avoid his and his brother's sentence of been hung and so makes its his mission to discover the identity of the man who gives Joss his orders. Mary tries to convince her Aunt to escape from Joss.