Set in the '90s, the dark flick tells the story of a young girl, Angela (Watson), who accuses her father, John Gray (David Dencik), of an unspeakable crime. Detective Bruce Kenner (Hawke) is assigned to investigate the case, and psychologist Dr. Raines (David Thewlis) is brought in to help Gray recall his memories of the event. However, what they eventually discover reveals a horrifying nationwide mystery.
Aside from a compelling storyline, the movie also features an unexpected Harry Potter reunion—Watson's castmate, Thewlis, played Professor Remus Lupin alongside her in the iconic series. Watch the trailer above, and catch Regression when it hits theaters Aug. 28.