In England, American exchange students Bill and Ronnie and their Danish schoolmate, Ingrid Jorgensen, take a tour of the fourteenth century Ambrose castle, built by the fourth Earl of Ambrose. After the castle’s current owner, the sixteenth earl, exhibits several portraits of his ancestors, he declares the castle has long had a reputation of being haunted. Bill is skeptical whereas Ingrid believes ghosts may exist. Ronnie, who must write an article on the castle for the college newspaper, then suggests that the friends get proof that the apparitions exist by secretly remaining behind and spending the night in the castle. The trio hides in the castle’s graveyard until the last tourist bus departs and the earl and his groundskeeper, Parker, retire for the night. The students creep back into the castle and upon returning to the main hall lined with the Ambrose portraits, an unseen voice bellows at them and the door slams, locking them inside. Terrified, the students watch in amazement as the fourth Earl of Ambrose materializes out of his portrait and steps before them. Ambrose assures the frightened students that he is a placid spirit, then reveals that the reason the ancestors haunt the castle is due to the tragedy of Sir Malcolm. Beheaded for leading an insurrection against King Henry VII, Malcolm was then condemned to wander the castle, his head separated from his body. Ambrose asserts that the only way the evil contained in Malcolm’s body can be driven out is for a special incantation to be uttered by a living person while simultaneously hurling a pouch, hidden inside a secret chamber unopened for four hundred years, at Malcolm’s portrait. Ambrose asks the students for their help and when they tentatively agree, he cautions them that he is only able to give them minimal assistance and warns that ancestor Sir Randolph enjoys haunting and will likely attempt to interfere. When Ambrose tells them that he is allowed to recite the incantation, in the form of a poem, only once, Ingrid agrees to memorize it. Ambrose vanishes after Ronnie attempts to photograph him and the students squabble briefly about their startling vision before Ingrid insists they begin searching for the secret chamber. Meanwhile, awakened by the noises from the castle, Parker reports to the earl and the men come to the castle gate. Hearing nothing, however, the earl dismisses Parker and returns to his cottage. The students split up, Bill exploring alone and Ronnie and Ingrid examining each of the great bedrooms. In one room, the couple is startled to hear the strangled cries of Lady Wingfield as she is murdered by her husband Charles for infidelity. Moments later Bill rushes in, panicked after a suit of armor threatens him with a large axe. Thoroughly frightened, the students decide to leave the castle and Ambrose materializes to plead with them to stay. Apologizing, the students insist they must depart, until they are abruptly addressed by an unfamiliar voice from the portraits. The speaker, Malcolm, insists that he will not let them depart until they have fulfilled their promise and freed his spirit. When Bill staunchly refuses, Malcolm paralyzes him until he relents. The students resume their search for the secret chamber and are amazed when they wander into a banquet room filled with celebrating ghosts eating and drinking boisterously. At the main table, Ambrose sits with Sir Randolph and the headless body of Malcolm. Randolph welcomes the students and announces that he forbids their mission as he intends to remain merry for eternity. Ambrose quietly warns the trio not to be taken in by Randolph’s temptations of pleasure and points out that the party has been going on for centuries and has grown quite dull. When Randolph orders a captive slave girl to begin a seductive dance, Ambrose again advises the students to ignore the entertainment and, slipping away from the table, leads them to the hidden entrance of the secret chamber. Using a single candle to light their way, Bill, Ronnie and Ingrid wander along a passage until they enter a dark, empty room holding nothing but a chest. Flinging open its lid, the students are frightened by a large snake, but Bill decapitates it with a nearby axe. Seizing the small pouch inside the chest, the students dash back to the main hall. Outside, however, Parker rouses the earl, insisting he has heard more cries and noises. Although angry, the earl agrees to check again and hearing the noise from Randolph’s banquet, orders Parker to summon the police. Two constables, led by Sgt. Grayson, soon arrive at the castle and accompany the earl inside. Discovering Bill, Ronnie and Ingrid, Grayson attempts to arrest them and dismisses their pleas to be allowed to complete their quest. When Grayson demands to see the pouch, Bill and Ronnie order Ingrid to fulfill their promise as they hold back the earl and constables. Ingrid dashes to Malcolm’s portrait and recites the incantation and hurls the pouch at the frame. Seconds later the group is mesmerized by the appearance of Malcolm’s body running down the stairs toward them. Malcolm’s floating head then appears from a corridor and joins its body. With a happy sigh, the reunited figure recedes into his portrait and disappears. Amazed, the students relate their experience and the earl promises not to press charges.