After witnessing a bizarre, traumatic incident involving a patient, a psychiatrist becomes increasingly convinced she is being threatened by an uncanny entity.
 
The tagline for this film is 100% correct - Once you see it, it's too late.  There are images from this movie that will haunt you for the days that follow.
 
FUN FACT:  A couple of days before the September 30, 2022 release, actors from the film showed up at various baseball games, sitting behind home plate dead still and smiling while staring into the camera, unmoving despite fans in the audience being understandably concerned, while wearing Smile shirts. Another soon appeared in the background with the crowd during the Today show.