A corrupt opportunist commits brutal crimes in the name of God and country in this atmospheric period horror tale. In 17th century England, as a people's uprising threatens Lord Cromwell's rule, superstition still rules the land, and the Royalists use this to their advantage by inaugurating a reign of terror in the name of wiping out alleged witches and agents of the dark arts. Matthew Hopkins (Vincent Price) has been appointed "witchfinder" by Puritan Royalists, and with the help of his thuggish assistant Stearne (Robert Russell), Hopkins travels from town to town, brutally interrogating those accused of witchcraft and using fire, drowning, and torture to extract "confessions" from the accused. Of course, Hopkins' opinions can be swayed with money and other considerations, and when Father Lowes (Rupert Davies), a priest whose sympathies do not lie with the Royalists, is arrested and tortured by Hopkins and Stearne, his devoted niece Sarah (Hilary Dwyer) is able to stay his punishment by sleeping with Hopkins. Sarah, however, is engaged to marry Marshall (Ian Ogilvy), a soldier in Cromwell's army, and once Marshall learns that the woman he loves has been seduced by Hopkins -- and raped by Stearne -- he becomes determined to expose the witchfinder and punish him for his misdeeds. Witchfinder General was released in the United States by American International Pictures, who in addition to arranging for Vincent Price to play Matthew Hopkins, changed the North American title to The Conqueror Worm, after a poem by Edgar Allan Poe which was read over the credits by Price, though the story bears no real relation to Poe's work.
~ Mark Deming, All Movie Guide