East Anglia, 1645. With the Civil War raging, much of England is in a state of near anarchy. Richard Marshall, a trooper in Cromwell's army, is ribbed by his friend, Trooper Swallow about his lover, Sara. When the party pause for rest, they are ambushed by loyalists. The ambushers are hunted and killed, but only Richard's awareness prevents one from killing Captain Gordon.

Richard takes leave to visit the village of Brandeston, where he is greeted by John Lowes, a priest and Sara's uncle. Lowes has been the victim of rising anti-Catholic feeling and, concerned for Sara, he agrees to consent to her marriage if Richard promises to take her from Brandeston. Richard agrees, and that night he and Sara make love.

In the morning, Richard departs, promising to return soon. On the road, he passes a lawyer, Matthew Hopkins, and his servant, John Stearne, who say they have business in Brandeston. Hopkins visits the church, where, urged on by villagers, he accuses Lowes of idolatry and consorting with devils. When Lowes refuses to confess, Stearne, on Hopkins' instruction, 'pricks' him with a large needle to find the devil's mark. Alerted by a neighbour, Sara rushes to the church, where she encounters Hopkins. Hoping to save her uncle, she agrees to allow Hopkins to visit her room that night, where he promises to hear evidence of Lowes' innocence. Hopkins agrees to suspend the torture and place Lowes in the jail, and that night, he visits her as agreed, and she reluctantly offers him her body.

The next morning, Hopkins rouses the drunken Stearne in the tavern and informs him he will be leaving the village for a short while, leaving Stearne to continue the search for witches. In Hopkins' absence, Stearne visits Sara and rapes her. When Hopkins returns, he and Stearne visit the jail, where Stearne extracts the remaining 'confessions' by torture. Hopkins leads the unfortunate 'witches', including Lowes, to the river, into which they are lowered with ropes - if they swim or float, they are guilty. One woman drowns, and is judged innocent; the others are found guilty, and hung. Their work done, Hopkins and Stearne leave Brandeston.

Richard, on a mission to buy horses, learns of the witchhunt and hurries to Brandeston. Marrying the traumatised Sara in an impromptu ceremony, Richard vows revenge on Hopkins and Stearne. He returns to his regiment, telling Sara to flee to Lavenham.

Richard tracks Stearne to Oxney and attacks him, but Stearne flees on horseback. Stearne meets Hopkins, and the two successfully evade the pursuing Richard. Returning to his regiment, Richard is warned that further absence may lead to court-martial.

Hopkins and Stearne are confronted by Swallow and other troopers, who demand their horses. After a scuffle, Hopkins gets away, but Stearne is captured. He subsequently escapes, but is shot and wounded in the shoulder. Meanwhile, Hopkins arrives in Lavenham, where he engages a local landlord to assist his work. Sara watches in horror as Hopkins oversees a 'witch' burning in the town square. Stearne arrives in Lavenham bent on revenge on Hopkins for abandoning him, but Hopkins pacifies him with money, and when the two men spy Sara, they are reunited, realising that Richard must join her soon.

Richard, honoured for his bravery, is despatched by Cromwell to find the King, rumoured to be planning escape by boat. The King evades them, but Richard learns that Hopkins is in Lavenham, and heads there, with Swallow and another trooper behind.

In Lavenham, Richard and Sara are captured by Hopkins and Stearne, who produce 'witnesses' to support charges of witchcraft against them. They are taken to the local castle, where Sara is tortured by pricking. Despite her agony, Richard refuses to confess, swearing to kill Hopkins. Swallow and his partner track them to the castle and kill the guards. Richard exploits his captors' panic to break free, and kills Stearne. Grabbing an axe, he frenziedly hacks at Hopkins. Entering the dungeon, Swallow is appalled at Richard's bloodlust, and ends the dying Hopkins' suffering with his pistol. Deprived of his revenge, Richard cries out in rage, his screams mixing with Sara's own howls of horror and madness.