Flashback

Fred Fitzell (Dylan O'Brien) is living his life just going through the motions, slaving away at his corporate office job. When talking with some friends from his time in high school, Fred remembers Cindy (Maika Monroe), a girl from his past who suddenly disappeared around the time a drug called Mercury ran rampant throughout their school. Desperate to figure out what happened to Cindy, Fred does Mercury, sending him on a trip that brings his mind to the past, causing him to struggle to discern what is real, and what isn't, as he begins to unravel the mystery behind her disappearance.