Elizabeth Sawyer is a poor, lonely, and unfairly ostracized old woman, who turns to witchcraft after having been unjustly accused of it, having nothing left to lose. A talking devil-dog Tom (performed by a human actor) appears, becoming her familiar and only friend. With Tom's help, Sawyer causes one of her neighbours to go mad and kill herself, but otherwise she does not achieve very much, since many of those around her are only too willing to sell their souls to the devil all by themselves. The play is divided fairly rigidly into separate plots, which only occasionally intersect or overlap. Alongside the main story of Elizabeth Sawyer, the other major plotline is a domestic tragedy centering on the farmer's son Frank Thorney. Frank is secretly married to the poor but virtuous Winnifride, whom he loves and believes is pregnant with his child, but his father insists that he marry Susan, elder daughter of the wealthy farmer Old Carter. Frank weakly gives in to a bigamous marriage but then tries to flee the county with Winnifride disguised as his page. When the doting Susan follows him, he stabs her. At this point, the witch's dog Tom is present on stage and it is left ambiguous whether Frank remains a fully responsible moral agent in the act. Frank inflicts superficial wounds on himself, so that he can pretend to have been attacked, and attempts to frame Warbeck, Susan's former suitor, and Somerton, suitor of Susan's younger sister Katherine. While the kindly Katherine is nursing her supposedly incapacitated brother-in-law, however, she finds a bloodstained knife in his pocket and immediately guesses the truth, which she reveals to her father. The devil-dog is on stage again at this point, and "shrugs for joy," according to the stage direction, which suggests that he has brought about Frank's downfall.
Frank is executed for his crime at the same time as Mother Sawyer, but he, in marked contrast to her, is forgiven by all and the pregnant Winnifride is taken into the family of Old Carter. The play thus ends on a relatively happy note—Old Carter enjoins all those assembled at the execution, "So, let's every man home to Edmonton with heavy hearts, yet as merry as we can, though not as we would."
The note of optimism is also heard in the play's other main plot, centering on the Morris dancing yokel Cuddy Banks, whose invincible innocence allows him to emerge unscathed from his own encounters with the dog Tom; he eventually banishes the dog from the stage with the words "Out, and avaunt!"
Despite the optimism of the play's ending it remains clear that the execution of Mother Sawyer has done little or nothing to purge the play's world of an evil to which its inhabitants are only too ready to turn spontaneously. Firstly, the devil-dog has not been destroyed, and indeed resolves to go to London and corrupt souls there. Secondly, the village's voice of authority, the lord of the manor Sir Arthur Clarington, is represented as untrustworthy, and Mother Sawyer utters a lengthy tirade indicting his lechery (he has previously had an affair with Winnifride, which she now repents) and general corruption, a charge which the play as a whole supports.
The Witch of Edmonton may be very ready to capitalize on the sensational story of a witch, but it does not permit an easy and comfortable demonization of her; it presents her as a product of society rather than an anomaly in it.
