This is a case of filmmakers who were just too cute for their own good. Banshee starts out as a car movie like The Fast and the Furious and, aside from the car chases never seeming to get above 35 miles an hour, it seems to be doing a pretty competent job. Then the movie takes a hard left turn and turns into a horror film and then slides into being a serial killer flick. I can understand why this sort of high concept genre bending might have appeared to be a good idea but Banshee doesn't quite turn out like combining chocolate and peanut butter. It's more like spinach and Pop Tarts.
Sage Rion (Taryn Manning) is the best car thief in town and one of those characters where everyone else in the movie can't stop talking about how awesome they are. After exhaustively establishing that she's all cool and quirky and tormented by personal demons, Sage ends up stealing car that belongs to a serial killer. He kidnaps one of her friends. She tries to return the car, which puts her on the bad side of her criminal boss (Tony Calabretta), and winds up a suspect in one of the killer's murders. That brings in a pair of cops who might as well be the guys from Dumb and Dumber for as useless as they are. While on the run from everyone, Sage learns that yet another of her friends has been kidnapped by the killer and stumbles into a rescue attempt that ends with her committing at least 2nd degree murder and no one giving a damn about it.
Aside from Sage and one of the cops chasing her teaming up to catch the serial killer as though it were the most normal thing for two strangers from opposite sides of the law to do, Banshee isn't terrible for the most part. It does overdo the girl power bit with Sage kicking ass like a combination of Jackie Chan and Hulk Hogan in a 'roid rage. And, of course, after making her out to be a living weapon, the plot then needs her to be as easily overpowered as a newborn kitten. The two cops are also so atrociously written that you can only explain their behavior as the product of multiple personalities, each one stupider than the last.
But car movies are about two things; chases and a cool main character with a checkered past. Banshee has a couple of decent chase scenes, if you can overlook how slow everyone is actually driving, and Taryn Manning has just enough spunk to make Sage worth watching. When the horror twist gets thrown in, it seems like just that little extra something to set this story off on an exciting and unexpected direction. However, as it veers off into serial killer territory, Banshee loses its structural integrity. The horror element could have coexisted with the car movie genre. The serial killer stuff just obliterates everything else. Nothing from the first half of the film has any dramatic or emotional relevance to the second half. As I mentioned, the main characters in car movies almost always have checkered pasts they have to overcome in order to save the day in the end. But once the crazy mass murderer enters the scene in this film, Sage's checkered past become kind of immaterial. Her personal demons are no longer the main problem in her life and when the story continues to focus on them, it comes off rather silly.
The folks who made Banshee thought they had a great idea and I'm sure it all made sense in theory. Unfortunately, when put into practice it works about as well as taking out someone's appendix with a garden trowel.