The film is a period piece set in Cornwall in 1819; the real Jamaica Inn still exists, and is a pub on the edge of Bodmin Moor. The score was written by Eric Fenby.
In 1819, Jamaica Inn is the headquarters of a gang of wreckers led by the innkeeper Joss Merlyn (Leslie Banks). The wreckers are responsible for a series of engineered shipwrecks in which they extinguish coastal warning beacons to cause ships to run aground on the rocky Cornish coast. They then kill the surviving sailors and steal the cargo from the wrecks.
The beautiful young Irishwoman Mary Yellan (Maureen O'Hara) is travelling to Jamaica Inn in a carriage, but the driver is afraid to stop there and drives a long way past the inn in spite of her repeated demands that he stop. Instead, he drops her off near the home of the local squire and justice of the peace, Sir Humphrey Pengallan (Charles Laughton). She meets him and requests the loan of a horse so she can go back to Jamaica Inn. Pengallan warns her not to go there. Nevertheless, Mary says she just came from Ireland, and as the orphaned niece of Joss's wife Patience (Marie Ney), she intends to live at Jamaica Inn. Unable to convince her to stay, Pengallan accompanies Mary to Jamaica Inn.
When Joss meets Mary, he tries to kiss her and push himself on her. Patience is distraught to learn her sister, Mary's mother, has died. When Mary tells Joss that Pengallan has accompanied her to Jamaica Inn, Joss goes upstairs and reports to Pengallan. We learn that Pengallan is the secret criminal mastermind behind the wrecking gang, who finds out when well-laden ships are passing near the coast, determines when and where the wrecks are to be caused, fences the stolen cargo, and uses the booty to support his lavish lifestyle, passing a fraction of the takings back to Joss and the gang.
In another part of the inn, the gang convenes to discuss why they get so little money for their efforts. They suspect Jem Trehearne (Robert Newton), a gang member who has been with them for only two months, of embezzling goods. They hang him from one of the rafters of the inn, but when they leave, Mary cuts the rope and saves his life. Trehearne and Mary flee the gang, narrowly avoiding recapture by swimming for their lives.
The next morning, they seek the protection of Pengallan, unaware that he is the secret leader of Joss's gang. Trehearne reveals to Pengallan that he is actually an undercover law-officer on a mission to investigate the wrecks. Pengallan is alarmed, but maintains his composure and pretends to join forces with Trehearne. Mary overhears this conversation and goes to the inn to warn Patience that she must flee in order to avoid being arrested as an accomplice. However, Patience refuses to leave her husband. Trehearne and Pengallan also go to the Inn to search for evidence. While Trehearne is searching the Inn, Joss and the gang return. Pengallan takes Joss aside and tells him a wrecking must be performed immediately because he needs the money to escape to France. He advises Joss to go into hiding too, as soon as the wreck is complete. Joss and the gang go to cause the wreck, leaving Trehearne tied up. Joss also seemingly ties up Pengallan so that his gang will not suspect their connection, but secretly leaves Pengallan's hands free.
After the gang leaves, Pengallan releases himself from his bonds and reveals himself to Trehearne. He gives Patience a loaded pistol and instructs her to shoot Trehearne if he gets loose, then leaves. Trehearne reasons with Patience, promising to let her and Joss escape if she releases him. She agrees and unties him. He sets out for a nearby military camp to get backup. Meanwhile, Mary goes to the wrecking site and re-lights the warning beacon which the wreckers had extinguished. The crew of the ship see the light and avoid the rocks. The gang resolve to kill Mary for preventing the wreck. Joss, who has developed a reluctant admiration for her, rescues her and the two escape by horse-cart, but Joss is shot in the back and collapses when they reach Jamaica Inn. As Patience is about to tell Mary that Pengallan is the secret leader of the wrecking gang, Pengallan shoots and kills Patience from offstage. Joss then dies of his wound as well. While Mary is reeling from the shock of witnessing these two violent deaths, Pengallan takes her hostage, ties and gags her, and tells her that he plans to keep her now that she has no one else in the world. He drives her, still tied up and covered by a heavy cloak, to the harbor, where they board a ship bound for France.
The gang returns to Jamaica Inn to find Joss and Patience dead. Just then, Trehearne arrives with a posse of soldiers, who take the gang into custody. Trehearne goes to the harbor with some of his soldiers to rescue Mary, and Pengallan is cornered on the ship. He climbs to the top of a mast, where he clumsily drops his gun. As the soldiers climb up after him, he jumps to his death, shouting "Make way for Pengallan!" Trehearne leads Mary away from the scene, and Pengallan's horrified butler Chadwick (Horace Hodges) is left wondering to himself, with a memory of Pengallan's imperious voice ringing in his ears.Charles Laughton – Sir Humphrey Pengallan
Leslie Banks – Joss Merlyn
Maureen O'Hara – Mary Yellen
Robert Newton – James 'Jem' Trehearne
Marie Ney – Patience Merlyn
Horace Hodges – Butler (Chadwick)
Hay Petrie – Groom (Sam)
Frederick Piper – Agent (Davis)
Herbert Lomas – Tenant (Dowland)
Clare Greet – Tenant (Granny Tremarney)
William Devlin – Tenant (Burdkin)
Emlyn Williams – Harry the Pedlar
Jeanne de Casalis – Sir Humphrey's friend
Mabel Terry-Lewis – Lady Beston
A. Bromley Davenport – Ringwood
George Curzon – Captain Murray
Basil Radford – Lord George
Wylie Watson – Salvation Watkins
Besides Laughton and O'Hara, secondary characters are played by several notable stage-and-screen character actors of the time, including "bruiser-type" actor Leslie Banks (who played General Zharov in The Most Dangerous Game) as Joss Merlin, and Robert Newton in an uncharacteristic role as Jem Trehearne, a suave young secret-police agent.
Charles Laughton was a co-producer on this movie, and he reportedly interfered greatly with Hitchcock's direction. Laughton was originally cast as Joss, but he cast himself in the role of the villainous Pengallan, which was originally to be a hypocritical preacher but was rewritten as a squire because unsympathetic portrayals of the clergy were forbidden by the Production Code in Hollywood. Laughton then demanded that Hitchcock give his character greater screen time. This forced Hitchcock to reveal that Pengallan was a villain in league with the smugglers earlier in the film than Hitchcock had initially planned.
Laughton's acting was a problem point as well for Hitchcock. Laughton portrayed Pengallan as having a mincing walk, to the beat of a German waltz which he played in his head, while Hitchcock thought it was out of character. Laughton also demanded that Maureen O'Hara be given the lead after watching her screen test (her acting in the screen test was sub par, but Laughton could not forget her eyes). After filming finished, Laughton brought her to Hollywood to play Esmeralda opposite his Quasimodo in 1939 version of The Hunchback of Notre Dame, where she became an international star.
In March 1939, Hitchcock moved to Hollywood to begin his contract with David O. Selznick. Thus Jamaica Inn was his last British picture, as well as one of his most successful.
Critics disparaged the film, largely because of the lack of atmosphere and tension which was present in the book, with its light-hearted, often camp banter, and portly landlord, far-removed from the darker characters and sinister inn and coastline depicted in the book. Today it is considered one of Hitchcock's worst films. Hitchcock himself was disgusted with the film even before it was finished and stated that it was a "completely absurd" idea. However, the film still garnered a large profit (US$3.7 million, a huge success at the time) at the box office. Daphne du Maurier was also not pleased with the finished production and for a while she considered withholding the film rights to Rebecca.
In 1978, film critic Michael Medved gave Jamaica Inn a place in his book The Fifty Worst Films of All Time.