*Detailed plot & explanation. Complete SPOILER here*
Robert is a man tasked with house-sitting for another man's home. He instead drops off his friend Andre to do it for him, as Andre (who's injured & wearing an arm sling) could use some rest & tranquility, with free food & drinks. After entering the home, Andre reveals (via selfie video) that he's recovering from an accident which has given him a concussion & amnesia, he then explores the house, failing to notice the security cameras hidden in it. He does however discover some booze & a small amount of pot.
A female news reporter on TV mentions a dead woman found in the trunk of a local wrecked car, with no driver found. The victim had reportedly been violently tortured before being killed. The reporter also begins to mention a group of inmates being transported from one place to another, but as Andre walks past, he turns off the TV without looking at it or paying any attention to what the reporter said.
He gets a call from a woman named Rachel, and is observed by the cameras in the house as he prepares for a date with her. Night falls as Rachel arrives, she too is observed entering the house by a video camera across the street. She brings some food & wine, and they talk. Andre seems to recognize & remember her, but admits he doesn't remember what happened the last time they met. She insinuates it was romantic.
There's a knock on the front door. A man named Guy claims to be a neighbor, he also claims to be concerned about a phone call he received at his home, allegedly from the police who were warning people in the area of escaped convicts. They believe it could have been a prank call, but Andre goes down the hall to ensure the house is secure. While Guy is left alone with Rachel, he acts rude & crass to her, before intimidating her into leaving. Andre returns, then he kicks Guy out for ruining his date & being obnoxious.
Andre's phone battery dies, yet his charger is missing, so he searches for the house phone to call Rachel. He finds a working land line down stairs, but the call only goes to her voicemail. He then discovers, next to the phone, a manila folder containing numerous surveillance photos of Rachel shopping around town. He then calls Robert, believing this is an elaborate prank, and questions Robert about who owns the house, & how the owner of the house has photos of Rachel. Robert assures Andre the house is owned by a friend, it's not a prank, & the photos are of another woman, convincing Andre that he's merely having paranoid delusions as a side-effect of his head trauma (his doctor said this may happen). Robert then reminds Andre this is a legitimate job, with the obligation of staying in the house. Andre calms down & gets stoned with the weed he discovered earlier. He has a paranoid psychedelic trip before going to sleep.
It's still dark when Andre wakes up to a noise, & discovers his video camera plugged into the TV downstairs. He rewinds it to see footage of himself sleeping, proving that someone was in the house recording him as he slept. Andre becomes angry at what he believes to be a joke which has gone too far, while searching & securing the house again. He then decides to just leave the house, but changes his mind after seeing someone outside in the darkness, after looking through the door's peephole. Andre then arms himself with a butcher knife, and discovers a bottle of Jagermeister in the freezer, beneath a bucket of ice.
As he pours a drink, a USB thumb drive spills out of the bottle. He explores the drive. On it is a folder of photos, & a single video file. The photos are of numerous women taken from afar, Rachel among them, then some close-ups, and gruesome photos of the women dead. Then he begins to watch the video. In it, a woman in lingerie is willingly handcuffed & blindfolded as an unidentified man teases her. The man then pulls out a scalpel, & slices the woman's tongue in half. As she screams in the video, the power in the house goes out, stopping the video & leaving Andre to blindly search for the flashlight he had earlier.
Andre finds the flashlight, & begins searching outside the house, where he is then attacked & chased back into the house by a man in heavy camouflage. The lights come back on as several police officers tackle him & handcuff him. Andre tells the officers he's only house-sitting for a friend, he professes his innocents, & encourages the police to play the video of the actual killer.
The woman on the video is violently tortured & killed, and when the camera pans up it's revealed to indeed be a blood-covered Andre.
The conclusion is, the home actually belongs to Andre himself, the photos of Rachel by the phone were from when he stalked her before the accident. The accident which resulted in his amnesia, happened in a car when he was attempting to dispose of his previous victim, while Rachel was to be his next intended victim. Guy is actually an undercover detective who pretended to be a neighbor in order to extract Rachel from the surveillance. It was all a sting operation to catch a serial killer, and the USB drive was the exact evidence they were hoping to find the entire time. Presumably it wasn't discovered during a warrant search, but now there's concrete evidence of multiple murders.
In the last sequence, Andre is revealed to have split personality disorder. Upon realizing his fate, his evil killer persona Andy emerges, with full recollection of all past murders, while cursing his passive & polite Andre persona with disdain. As he's led to the car, Andy passes a crying Rachel, who's presumably in shock at how close to death she had come, and his friend Robert, who presumably agreed to cooperate with the police at the hospital after being told of the crimes being investigated.
... The end.