The story is basically about jealousy. Two cousins, Hannah who is sweet and Sienna who is completely unstable. Their in high school and Sienna's boyfriend Roger Johnson dumps her a week before Prom and ends up asking out Hannah instead.

Sienna is telling this story to Maya, Hannah's daughter later in the movie (after she's wormed her way into their household after Hannah's 'demise', which is so shocking and sad) but omits the fact to Maya that it was actually Tony (Maya's dad) that had dumped her and asked Hannah out instead.

The actress who plays Sienna is a red headed stunner and she plays her very soft and sweet in some scenes, but then she turns on a dime, acting quietly psychotic with moments of crazy outbursts. Her goal is to replace Hannah, she wants Tony, the kids, (Maya also has a younger sibling named Luke),the house, and the money.

Sienna proceeds to 'take out' or eliminate completely, the female competition in the house. Janet the elderly caretaker of the house, who cooks, cleans, helps the children with their homework and takes them to school and back, is pretty much replaced by Sienna who takes over all these duties on the very first day. Janet immediately does not trust her and Sienna senses this and spikes her coffee one morning with something that affects Janet's long sobriety. Which in turn, does not allow her back in the house or to care for the children.

Sienna then starts to feel threatened by Lauren. Tony's very attractive blond Office Manager at where he works as a Cardiologist. Her actions are very unnerving, scary, and just plain evil to anyone who crosses her path.

Maya starts to get suspicious of Sienna and talks to her dad. At this point it becomes frustrating that he doesn't believe his daughter, which makes him the dumbest or most naive man in the world. But Sienna is that good about being duplicitous. She can shed a tear on the drop of a hat and has an answer to everything.

This all leads to Maya's (and Sienna's!) biggest event in High School - Prom night!! Maya is so excited that sweet Jake has asked her. The lengths that Sienna goes to, to replicate her own missed Prom night with Tony, is really creepy. The ending was suspenseful and had a happy outcome for all, except one person. You can take one guess who that is.

The Acting is absolutely embarrassing and hard to watch. The script is terrible. The worst of the acting is from the one who is apart of a family of actors.

Ever since high school, Sienna Lawton was envious of Hannah, who was the belle of the ball at senior prom when Sienna was a sophomore. Hannah went on to marry Dr. Tony Wilson, a distinguished cardiologist.

For years, Sienna was seething with jealousy. Then, she acted on her sick impulses. Hannah met a watery death when Sienna pushed her over overboard knowing that Hannah could not swim. Later, Sienna tried to explain: "I didn't mean to push her!"

"Killer Prom" is a by-the-numbers formula film about a crazed obsessive-compulsive who worms her way into the life of the Wilsons. After the death of Hanna, Sienna lies about trying to get a realtor's license and moves in with the family. She administers a roofie to the nice nanny, Janet, who is subsequently fired for drunkenness. She also murders Dr. Wilson's loyal assistant Lauren because she fears competition.

Sienna has a special place in her deranged mind for the wonders of prom night. She goes through an elaborate ritual to set up the grand moment when she will become Mrs. Tony Wilson in an improvised prom setting.

But it is the perceptive daughter Maya who first gets wise to Sienna's game. Maya shrewdly phones Sienna's mother, Dorothy Lawton, and discovers that Sienna was always jealous of Hannah. The heroic Maya then alters her plans on prom night to rescue her dad from the evil clutches of Sienna.

One of the more interesting characters was Jake, the date of Maya on prom night. Jake selflessly supports Maya in discovering the truth about Sienna. Despite the routine nature of the film, the cast was great with all of the actors delivering convincing performances.

At least the filmmakers devised one of the most unorthodox prom nights imaginable that occurred at the Wilson residence courtesy of Miss Sienna Lawton.