Jason Yu takes a simple, relatable fear and squeezes it tight. Most of the film happens in one small flat, mostly at night, and the tension comes from waiting for the lights to go out. Every bedtime becomes a scene of dread.
Jung Yu-mi is outstanding as Soo-jin. She goes from loving, practical wife to sleepless, terrified mother to something much wilder, and every step feels earned. Lee Sun-kyun is warm and gentle as Hyeon-soo when awake, which makes his night-time behaviour even more unnerving.
The film keeps two explanations alive at once. Is it a medical sleep disorder, or is something supernatural inside him? The script plays fair with both, and the balance is clever. There is also a sharp streak of dark comedy, especially in the final act.
At just 95 minutes, it is tight, smart and never wastes a scene. Some viewers may find the ending too open, but that is part of the point. It is one of the best Korean horror films of the 2020s.
