Against the Night (2017)

Rachel, the sole survivor of an incident at the abandoned Holmesburg Prison, is being interviewed in the prison by Detective Ramsey. Hours earlier, during a housewarming party, Rachel's wannabe filmmaker friend, Hank, convinced Rachel and seven others to help him make a ghost hunting video at Holmesburg. After breaking into the building, the group splits up to explore it, with Rachel and her ex-boyfriend, Sean, uncovering paperwork relating to human experimentation, as well as unintelligible blueprints for structures similar to Holmesburg.

The filmmakers are stalked and picked off one by one by a figure wearing a gas mask and a Hazmat suit. Hank is convinced that the murderer is an alien, reveals that Holmesburg is a hotspot for extraterrestrial phenomena, and postulates that the prison's true purpose is to act as something akin to a landing pad for otherworldly beings visiting Earth. Hank and two others are all killed at the same time by the murderer, who binds, gags, and places gas masks on Dan and Michelle, which leads to the latter being accidentally killed by Sean.

After Rachel and Sean find and free Dan, the three discover a Methamphetamine laboratory on the prison property, where they recover Dan's cellphone. The trio call for aid and seemingly kill the masked man, only for another to appear and kill Dan. Rachel and Sean flee into the laboratory, where they find a bunch of dead drug cooks and dealers right before Sean accidentally attacks and is shot by a SWAT Team.

Detective Ramsey has doubts about Rachel's story, as he and his fellow officers have found no signs of there being anyone else in the prison besides the methamphetamine dealers, all of whom were dead before Rachel's group broke in Holmesburg. Detective Ramsey posits that Rachel and her friends all unknowingly became high on methamphetamine fumes, which led to one or more of them potentially killing each other during psychotic breaks, right before another officer radios in to inform Detective Ramsey that they have recovered all of the footage that was shot by Hank's hidden cameras, and that, "It's not what we thought." The lights then go out, and gunshots and screams ring out as a figure wearing a gas mask enters the room and slaughters Detective Ramsey. The entity then removes its mask to reveal that it is an alien right before lunging at Rachel.