The opening credits of the arresting psychological thriller “ Ladyworld ” play out over the rumbling of an earthquake as it strikes an isolated mansion. When the tremors stop, the film opens to find the quake has cut off access to water, electricity and all paths outside. Eight teenage girls who came to the house for a birthday party are trapped.

The pragmatic Olivia (Ariela Barer) is voted by the group as their leader in a narrow victory over the vicious Piper (Annalise Basso), who nominates herself. Olivia tries to establish order in the house, encouraging the girls to pass a crystal when they want to speak. But Piper agitates the group around the unseen threat of a hiding man. The man could attack at any time, Piper insinuates, and the only answer is to become more frightening than him. As the situation in the house grows dire, with the girls unable to wash or eat, Piper draws more disciples into apocalyptic playacting — sometimes suggesting the sexual violence she exerts might come from the unknown man.