She is a chainsaw using serial killer, responsible for a series of murders involving naughty ladies of the night in the city of Pittsburgh. Early on in the film the killer is shown fully clothed with their face covered, so their identity is a mystery, as is the fact it is actually a woman responsible.
In the film, two hapless detectives, Sweeney Birdwell and Joe Blocker, are trying to solve a grisly series of murders involving women having parts of their body removed with power tools. The killers power tool fetish, involves carting along a portable generator to power them up. The weapons used are a circular saw, hedgetrimmer, industrial shop-vac, jackhammer, nail gun, and chainsaw. Joe reveals that he worked on a case exactly like this one, back in Las Vegas, and with the help of the daughter of the man he worked with back then, they try to solve the case.
Grace is first seen working as an awkward and clumsy roller skating waitress at a local Egyptian-themed restaurant. The movie's heroine thinks Grace is to be another victim of the killer and tries to save her, only for it to be revealed that Grace herself is the killer.
Her true self is finally revealed when the owner appears at her door to give her waitress lessons. He has ulterior motives in that he plans to photograph her in a skimpy outfit. She quickly turns the table on him and ties him up.
Grace captures the heroine, Deedee Fletcher (Susann Fletcher) and tortures her kidnapped father in front of her and tells her henchman to rape her. Some of the movie's heroes arrive in time and save their friend before she is raped. During a scuffle, Grace grabs the heroine and takes her outside where they have a fight, which Grace eventually wins by knocking the heroine out with an object.
She then hangs the heroine by the neck between a giant crusher, and places her foot on the button that prevents it from crushing. If she removes her foot from it then the heroine would be crushed. One of the cop heroes arrives outside and shoots at Grace, which doesn't kill her but causes her to release her foot, starting the crusher. The heroine pulls Grace inside the crusher with her and they fight briefly before the heroine climbs to safety and Grace ends up being crushed to death.