At the end of The Blue Room (2014), Julien (Mathieu Amalric) and his mistress Esther (Stéphanie Cléau) are both arrested for conspiring together to poison Julien’s wife, Delphine (Léa Drucker). The film intentionally leaves it open as to whether or not either of them truly had responsibility in the death. The film is a “whodunit” without being one; it’s a tragedy foremost, with a murder mystery underneath.

However, the film gives nice clues as to who the real murderer was, brought out subtly through subtext and a character’s moment of sudden awareness. My interpretation is this:

During the film, Esther’s husband died of “natural” causes. This is what the film says, and likely the truth, though there’s no way to know. Esther’s mother-in-law, Evelyne (Véronique Alain), who was apparently aware of Esther’s adulterous relationship with Julien, does not agree it was natural and blames Esther for the death. She believes Esther killed him to be rid of him. This is made clear by Evelyne outright saying so during her court testimony in the film’s final minutes. She then cryptically adds, “I hoped they’d turn on his wife next,” looks at Julien, and continues “And that happened, didn’t it?”

As Evelyne speaks, recounting how the box of jam was picked up at the pharmacy by Julien and insisting nobody at the pharmacy had tampered with the parcel, the camera lingers on his face. When her testimony is finished and she leaves the courtroom, she glares at Julien, and his expression changes as if he’s had a moment of realization.

She poisoned the jam. She framed both Esther and Julien to get back at Esther for what she believed she’d done to her son. And it worked. Esther hardly cares, her final piece of dialogue mentioning that her and Julien will now be together forever (in jail), and Julien’s face conveys feelings of confliction. He didn’t technically kill his wife, but his affair did. He’ll continue on as a man tormented by the guilt of his decisions.

Ignore the fact the two get sentenced on what, in reality, is almost completely circumstantial evidence, and it makes for a poignant ending to the story.