Warning: Spoilers ahead for the ending of Prime Video’s “We Were Liars.”

In the last three episodes of “We Were Liars,” Prime Video’s new psychological-thriller series, the long-running mystery finally unravels, and Cadence Sinclair Eastman learns the truth about what really happened on Beechwood Island during the summer of her accident.

As her memory returns, so does the unbearable reality: Her three closest friends — Mirren, Johnny and Gat — died in a fire that they started together.

“It was a complete shock,” actor Shubham Maheshwari, who plays Gat, told TODAY.com. “In all the directions the story could have gone, it just completely made me a fool.”

Though the series is adapted from E. Lockhart’s bestselling young-adult book published in 2014, Maheshwari and his co-star Emily Alyn Lind, who plays Cadence, read the novel while auditioning.

“While I was reading the book, I didn’t see it coming at all,” Maheshwari said. “I think, or at least I hope, that the show kind of does that, too.”

So what actually happened with the fire, and how did Cadence come to remember it? Here’s how the ending of “We Were Liars” went down.

In the final stretch of the series, viewers see Cadence piece together what happened to her two summers ago, when she experienced an accident — one she couldn’t remember — on her family’s private island off the coast of Massachusetts.

In the penultimate episode, the timeline from two summers ago shows Cadence and the Liars around a fire, sifting through her grandfather’s will and the ways he’ll be distributing his wealth when he’s gone. Cadence then ponders a world where the “petty, material” things tearing the Sinclair family apart were just … gone. Cut to present-day Cadence, as the rest of the memory becomes clear to her.

“There was a fire,” she tells Mirren and Johnny. “We burned this place to the ground.”

The finale shows viewers what happened: Cadence, in a drunken stupor with the rest of the Liars, suggests they gas up every part of the house with fuel from the boathouse, light a match and get out of there. So they do just that — but the fire moves quicker than the Liars. Mirren and Johnny are trapped, Gat goes in to save them, and only Cadence escapes. Just when she realizes none of them made it out, the house’s gas line explodes, sending Cadence cascading into the ocean.

And all that time in the present day when Cadence was conversing with Gat and her cousins — it was in her head. She’s no longer simply a privileged teenager on a summer getaway; she’s a girl haunted by guilt.

Series creators Julie Plec and Carina Adly MacKenzie said they leaned into both the mystery and emotional fallout.

“It’s a complicated story,” Plec told TODAY.com. “Cadence has this jarring event, this terrible thing that happened to her. … It makes her unable to understand her truth.”

And, despite their privilege, the Liars’ choices are messy and real.

“You start with characters that the audience is going to want to reject and hate just for existing,” MacKenzie said. “And then you have to give the audience a reason to stick around and to pull back the layers on their pain and their trauma.”

At the series’ end, Cadence chooses to leave her family behind.

“Loyalty means doing one last thing to mourn — and also pay respect to her friends that are gone,” Lind told TODAY.com. “It’s the least that (Cadence) can do after everything that they have had to endure.”

As Cadence walks away from Beechwood Island, she’s not free of guilt — but she is reclaiming her voice.

Lind hinted that this isn’t the end of Cadence’s story: “Her grandfather threatens her and says, ‘If you do (leave), I will expose you for everything.’ And she decides to do so anyway.”

Whatever comes next, “We Were Liars” ends its first season on a chilling, cathartic note — where truth, memory and loss collide.