The film stars Sam Strike, Erin Moriarty, Kian Lawley, Robin Tunney, Virginia Gardner, Brandon Micheal Hall, Bill Engvall, Julian McMahon, and Lance Reddick.

After pulling off a successful burglary in broad daylight, Iris tells the other two that she has info on another possible job at a ritzy mansion near the coast.

Under the guise of caterers, the three meet with the mansion's owners, the Dawson family; father Patrick, mother Roxanne, son Elliot, and daughter Alexis.

These guests consist of musician Ollie, "blood brothers" Cameron and Jeremy, group leader Milo and his date Becca.

During the struggle, Iris kicks Ollie down the stairs, killing him, and the guests are held back by Milo's command to behave themselves.

Iris breaks free and discovers that Becca committed suicide before rushing into a closet downstairs, while Casper hides in a bedroom and arms himself with a revolver he found.

Attempting to deescalate the situation, Milo tells Casper that the group he leads consists of recovering serial killers who try to subdue their urge to kill through his leadership.

Enraged, Milo beats Jeremy to death, but is shot by Patrick, who intends to kill Iris and Casper, much to the dismay of Roxanne.

Alexis manages to hide Iris and Casper in a secret room, which contains photos of the group's members and a sealed off chamber.

Seeing his daughter's betrayal over the security cameras, Patrick uses the home's intercom system to play a music box tune which awakens Mikey, the Dawson's "dog," who is in the sealed chamber.

"[1] Noel Murray, of the Los Angeles Times, wrote in his review: "The darkly comic, blood-soaked thriller 'Monster Party' is a throwback to the post-Tarantino ’90s, when violent characters were treated like cartoons and any picture with fewer than a dozen corpses was practically for children.