The ending of Insidious: The Last Key explained

For its fourth installment, the Insidious franchise takes another step back in time. We see one of Elise Rainier's earliest childhood experiences with the other side—and then we see her as a full-grown ghost-hunter who's made to revisit her past in cruel and surprising ways. While the story is mostly a standalone adventure for the spiritual psychic, Insidious: The Last Key still draws on the mythology of the series, and features some of the central players of the franchise in fun and fresh new ways. 

Let's take a look at how Insidious: The Last Key explores Elise's devastating backstory and wraps things up on a note of continuity. 

There's a pattern of possession

In childhood, Elise is tormented by more than just the spirits that occupy her family home. Her prison guard father is also heavy-handed with punishment, to the point of abuse. Clearly deranged, he insists he can beat the ghostly visions out of her and fears her supernatural gifts. Summoned back to the property in her later years by the home's new occupant, Adam Garza, she discovers he's kidnapped and tortured a woman in the basement for months. He claims something has invaded his head before he's done away with by Specs—and afterwards, Elise continues to explore and uncover more terrible secrets about the history of the home, including her father's abduction and murder of a woman (and possibly others) in that very spot.

Elise surmises that Adam Garza and her father before him were both possessed by the demon that terrorized her in her youth. Given the opportunity to exact revenge upon her father in The Further by punishing him with the same stick that caused her so much pain while growing up, she ultimately relents and realizes that her father and Mr. Garza were simply feeding the demon the hate and hurt it needed to thrive. Although it's not clear that all of her father's bad behaviors were attributable to the demonic force, he apologizes to her in ghost form before withering back into his spiritual cell. 

Her mother's greatest weapon is love

Although Adam Garza is creepy enough to sustain some suspense in the second act of the film, the true big bad of the movie is the key monster. Elise first runs into him/it in childhood after her father banishes her to the basement as penance for her refusal to deny her visions. Perhaps he's possessed by the spirit and wants her to be down there at the time because she proves quite useful to the key demon. A voice summons young Elise to a keyhole that unlocks the door and allows the demon to escape its confines. Her mother is the first true victim of that mistake, as she attempts to rescue Elise from the basement but is instead killed by the nefarious spirit while Elise remains in a state of demonic hypnosis. 

Her mother's passing is a tragedy for Elise and her brother. A warm and loving parent, she'd given them a whistle to blow if they ever felt scared of Elise's sightings. As we see in Elise's older years, the whistle was lost for decades—but it pops up during her return to the old home, and it's used by the most tortured spirits to guide her throughout her battle, since the key demon deprives his victims of the ability to speak. When Elise confronts the demon in its lair, it outmaneuvers her and deprives her of her voice, too, but she finds the whistle in time to summon the spirit of her mother, who's able to vanquish the beast (although perhaps not permanently) through the sheer power of her love and light. It's not clear if her father or mother ever escape the otherworldly prison, but they do each seem more peaceful when Elise departs.

She coaches herself to continue on

One of the most surprising encounters Elise experiences during her time in The Further is when she runs into herself as a child, at the time just as her mother was being murdered in the basement by the key demon. She doesn't tell the child version of herself who she is, but does insist that young Elise use her gifts to help people, despite her father's tyrannical treatment. If only she'd been able to tip off the child that the girl she spots in the laundry room at the age of 16 is very real, and not another figment of her wild imagination as her father suggests, she might have been able to save Anna. Alas. She does at least encourage her to use her nightmares for the betterment of the world—and to never back down from demons, otherworldly or otherwise. 

Carrying on the family business?

Although Elise's brother is none too thrilled to see her again, decades after she'd escaped their father's menacing clutches, he doesn't have a choice but to welcome her once she rescues his daughter. After Elise informs Christian that she found his old whistle in the home, he decides the relic is important enough to track down. Problem is, his youngest daughter Melissa is summoned down to the basement by the key demon, who makes short order of adding Elise's niece to menagerie of victims. Elise senses the attack and returns to the property, promising to find her. After she's temporarily incapacitated below, though, Imogen decides to try her own hand at psychic work and is lulled into a state of hypnosis by Tucker and Specs. 

She's there on a rescue mission, but it's Elise who ultimately leads the ladies back to safety, and Christian is grateful for her salvation of his daughters. Meanwhile, Imogen has now tapped into her own paranormal gifts, and Elise's legacy can live on through another generation. 

Everything comes full circle

The movie finishes with a direct link to the timeline of the original Insidious movies. Elise dreams about a boy named Dalton being haunted by the red-faced demon we came to know so well in the earlier installments and sees Renai and Josh, lying in bed and lamenting the unknown that's troubling their child. Elise awakens to receive a call from Lorraine, who reminds her that she helped her son Josh (in the flashback events of Insidious 2), and now the same thing is happening to Dalton. That's the catalyst for the events of the first Insidious, of course, when Elise helps Dalton escape from The Further, only to be strangled by Josh, who's been possessed by the same demon that haunted him as a child.

Insidious 2 left off with Elise still working her demon-battling magic in The Further, following Tucker and Specs to new spectral assignments, but with the added element of Imogen, a new medium who can work with Elise, the ghostbusting business might not be done for the Insidious team just yet.