Plot

A prequel set before the haunting of the Lambert family that reveals how gifted psychic Elise Rainier reluctantly agrees to use her ability to contact the dead in order to help a teenage girl who has been targeted by a dangerous supernatural entity.

Go back to the beginning... in this chilling prequel that takes place before the unforgettable haunting of the Lambert family. When paranormal investigators Tucker and Specs team up with the psychic Elise to help a teenage girl contact her late mother, Elise is forced to venture back into The Further where she finds a ruthless supernatural entity craving the souls of the living. It's the darkest chapter yet in this spine-tingling portrayal of evil unleashed.—Sony Pictures

Years before the chilling haunting of the Lambert family in Insidious (2010), Elise Rainier, a gifted but weary psychic, reluctantly agrees to help troubled teenager Quinn contact her deceased mother. Of course, Rainier has warned the girl of the grave dangers lurking in the unknown. Instead, Quinn proceeds, only to attract unwanted attention and something malevolent. As pure supernatural evil latches onto her, Elise must summon the courage to venture into The Further, a ghostly dimension envious of the living and the material world. But there is no turning back now. And with Quinn's trapped soul in the balance, no one knows what it will take for the grizzled medium to confront the shadowy realm's monstrous creatures.—Nick Riganas

A prequel set before the haunting of the Lambert family. Elise Rainier reluctantly agrees to use her spiritual ability to contact the dead in order to help Quinn Brenner, a teenage girl whose mother Lillith has recently passed. Quinn believes that Lillith has been attempting to reach out to her through the spirit world, so she visits Elise for a reading. Elise is unable to complete the reading, she stops after hearing a demonic presence who threatens to kill her. She warns Quinn that if, "you call out to one of the dead,all of them can hear you."

Soon after the reading, Quinn begins to hear noises at night and notices more and more supernatural events occuring. She skips school to audition for a theater academy in New York. Before going onstage, she notices a figure waving to her from the offstage. This throws her audition off, and she stumbles through her lines. Later that night, Quinn meets with her friend Maggie. Maggie complains of her blown audition, and after they have a short conversation, both start feeling better. As they are crossing the street, Quinn sees the same figure waving down the street and stops to look. She is then hit by a car. The car accident leaves Quinn with two broken legs in casts. She is bound to a wheelchair. Her father, Sean, puts her in bed, with a bell to ring if she need him. Later in the night, she hears a knock on her wall. Assuming it is her next door neighbor Hector, she knocks twice. He copies her, and she knocks the "Shave and a Haircut" pattern. He finishes it. Quinn texts Hector, when he reveals that he isn't home. Fearing it was someone else next door, she turns the light off to go to bed. The bell rings itself, scaring her, and her dad comes in.

These paranormal occurances become more and more frequent, each time Sean comes in and saves her. The demon is seen more and more frequently: a demonic corpse with a breathing mask, making a deathly rattling noise. Sean finds her thrown from her bed, on an entirely different floor, etc. Eventually, a version of Quinn without a face, hands or feet, is seen following under the demon's command. The odd version of Quinn is found by Sean on the ground outside of a broken window. When Quinn attempts to look over the edge of the window to see, the demon grabs her and tries to pull her down. Sean saves her, but her neck is injured in the process. Sean attempts to get in contact with Elise. She reluctantly comes, but as she enters the spiritual realm she finds herself afraid, and the demon very nearly kills her. She is brought back to living world, terrified, and refuses to continue. Sean has no choice but to call in someone else, a pair of bloggers: Specs and Tucker. Meanwhile, Elise seeks solace from her friend Carl with her same "gift". Carl reassures her that she is much stronger than she believes.

After a terrifying experience with Quinn and her demon, the three men admit that there is no doing this without Elise. Elise is now willing to help, this time she is much more powerful and confident. She is easily able to defeat the demon, but as they are escaping, it grabs a hold of Quinn's limbless version. This version of Quinn is revealed to be the half of Quinn's soul that the demon controls. Elise returns to the living world, and tells the group that this part of the battle must be fought by Quinn alone. They all grab ahold of her, but it is shown that she is losing the battle against the demon, as her alternate version gains more of her features. Elise begins to hear a voice in the living world, leading her to Quinn's diary, revealing a letter that Lillith wanted her to see before she graduated. The power from this letter helps guide Lillith to save Quinn and banish the demon, returning her to the living world. Lillith leaves her with some parting words, and the family is finally back together, as Specs and Tucker join Elise to deal with other supernatural disturbances.

Elise heads home to find that her husband's spirit has left his sweater on the bed. Overwhelmed with emotion, she holds his sweater close. Her dog then begins barking into the darkness. Elise approaches the area he's barking at, where she discovers the presence of two supernatural entities.