In a gritty and alternate 1985 the glory days of costumed vigilantes have been brought to a close by a government crackdown, but after one of the masked veterans is brutally murdered, an investigation into the killer is initiated. The reunited heroes set out to prevent their own destruction, but in doing so uncover a sinister plot that puts all of humanity in grave danger.

The film shows Sabrina Spellman turning 13 years old and receiving her first magic wand from Enchantra. As custom for all witchlings, she enrolls in the Witch Academy to learn the three principles of witchdom (to use magic wisely, be true to one's friends, and be true to one's self). Feeling inferior because she's only a half-witch, Sabrina conceals her mixed heritage and manages to become popular. Sabrina joins her new friends in making fun of Nicole Candler, a "bookworm" who doesn't fit in. When Sabrina discovers that Nicole is a half-witch like herself, the pair become good friends. Sabrina's other friends figure something is going on between Sabrina and Nicole and set out to prove that Nicole is a half-witch. They accomplish this by levitating up to a tree outside and find the half star on her hand. Sabrina visits Nicole in her dorm room and together, they begin a journey to the witches' realm in hopes of becoming full witches.