In the episode, Cyd's dog, Diesel, accidentally consumes Barry's invented wolf-serum and becomes a half-wolf monster going after both Cyd and Shelby. During the encounter, Diesel hurls the serum at Cyd. The protagonists successfully travel back in time to prevent Diesel from getting into the serum, but during the preparation for the school's Halloween party, Cyd feels the effects of the serum and turns into a werewolf.
After letting out a demonic howl at a (fake) full moon, Cyd became a villainess and snarled at Shelby before going after her. The chase led Shelby to Barry's educational maze, where the evil Werewolf Cyd finds her with Barry and Naldo. The she-wolf trapped the trio in a dead end, where Shelby attempted to get through to Cyd, with success. Cyd regained control of her urges, but remained her werewolf form for the remainder of the episode.