Worm seems to have a terrible hold on Jessica, compelling her to do cruel and destructive things to people in her life who have upset her.

When Jessica finds herself contemplating Mrs. Fortune's murder, she realizes she is in danger of going too far, and decides to exorcise Worm herself in order to break his hold over her.

In a starred review Kirkus Reviews wrote "There's some danger that adults will be as spooked by Jessica as she is by Worm's evil eye, but the cat's bewitchment proves a perfect medium for a sensitive, sympathetic probing of a disturbed child's fears and anger -- and for a story that economically, seemingly effortlessly, captures the elusive eeriness of the supernatural.

"[4] In 1972, a New York Times review of the book noted, "Perhaps because she never underestimates the mystery, perhaps because she walks the thin line between real and phan tom worlds so knowingly, Mrs. Snyder's brand of fantasy is convincing on many levels.

"[5] The book has often been banned[6] from school libraries in the United States because of its focus on the subject of witchcraft, the description of visions or nightmares Jessica experiences, and its protagonist's disturbing inner monologues with Worm/herself.