On the night of an astronomical anomaly, eight friends at a dinner party experience a troubling chain of reality bending events.
Why it is hard sci-fi
Eight people at a dinner party on the night a comet passes overhead. The comet creates local decoherence between parallel branches of reality, and the houses on the street start to overlap. The film treats the many-worlds interpretation literally and works through the consequences in real time. The cast did not have a full script and improvised inside scenarios the director had constrained, which gave the film its experimental feel.
Science inside it
Many-worlds quantum mechanics as a working device. The film cites the 1923 Hessdalen comet incident as a precedent, invokes Schrodingers cat to set up the rules, and uses object permanence as a diagnostic. A character marks a glass to identify which version of the house they are in. That is a real protocol applied to an unreal situation.
Spoiler alert
The protagonist eventually realises she has crossed into a branch where her counterpart is unhappy and decides to murder and replace her. The final shot reveals that her own original self has done the same thing in a third branch and is calling her phone at breakfast. The film commits to the rule. There is no protected version of you.