Nous ne sommes pas seul·e·s au monde.

Mara returns to the isolated house of her brother Sam, who died a year earlier in an arson attack along with his daughter. Driven by an impossible grief, Mara has devised a crazy plan for revenge: to kill the culprit herself on this sinister anniversary, a former associate of Sam's who escaped justice. But during the night, a series of mysterious and frightening phenomena turn her plans upside down...