The Final Problem Ending Explained: Who Is The Killer

Netflix's Spanish murder mystery closes on a swapped identity, a wartime revenge plot and a detective who lets his killer walk free.

Spoilers ahead for The Final Problem, Netflix's four-part Spanish limited series that dropped on 25 September 2026.

The whole show hinges on one swap. Adela Figueroa, the wealthy guest trapped in a storm-locked hotel on the island of Santa Agueda, isn't Adela at all. She's Elisa Mander, the English tourist everyone believes died by suicide in episode one. Elisa was Adela's assistant, jealous of her money and her recklessness, and when the storm cut the island off from the mainland, she saw her opening.

Here's how it worked. Elisa struck the real Adela on the temple with a stool, then strung her up using the storeroom's pulley system so it read as a hanging. Everyone assumed the corpse was Elisa. She became Adela in every way that mattered, right down to fooling the other twelve guests trapped in the hotel.

Benjamin Basil, the ageing actor famous for playing Sherlock Holmes, isn't fooled for long. He notices Adela's fingers, worn the way a typist's would be, nothing like what you'd expect from old money. That's the thread he pulls. He restages the first murder on a film set built as an exact replica of the hotel storeroom, walking Adela and the audience through every clue he'd missed the first time round: the orange shawl used to drag the chair under the door, the deliberately weakened rope, the absent sand near the entrance.

The motive goes back to World War 2. Elisa's husband John, an RAF pilot, was shot down over Dresden, captured, and executed after a failed escape attempt. The order was signed by Hans Ludwig Klemmer, who walked free after the war and lived out a quiet life. Elisa found him at the hotel and killed him for it. She also killed Dr. Seruya, not part of the original plan, after he worked out the rope had been tampered with and tried to use that knowledge for himself.

There's history between Basil and Elisa too. Years earlier, Basil had strung her along with promises of film auditions, used her, then cut her off. Running into him on the island reopens that wound, and it's also what puts her at risk, since he's exactly the kind of man who'd piece the whole thing together. She nearly finishes him off by leaving him in a running car in a closed garage, but he'd already planned his own way out.

So it ends not as detective versus killer but as two people confronting a shared, ugly past. Basil has enough on Elisa to hand her to the police. He doesn't. He lets her go, on the understanding he'll use the evidence if she kills again, telling himself his own conduct pushed her here. The final image has both of them reading Arthur Conan Doyle's A Scandal in Bohemia, an obvious nod to Irene Adler, the one woman who ever got the better of Sherlock Holmes.

Netflix hasn't announced a second season, and as a limited series adapted from Arturo Pérez-Reverte's novel, The Final Problem doesn't leave an obvious opening for one. Whether Basil and Elisa's arrangement survives another case is anyone's guess for now.