The narrative unfolds with a clandestine meeting between Tony Falcone and Andree Despierre in the blue room, where they share an intimate moment. It becomes apparent that this memory is not in real-time but rather a recollection during an interrogation. The story weaves between past events and Tony's present situation, where he is being questioned about the circumstances surrounding a pivotal August day.

The Unfolding of Events

Judge Diem, a contemporary of Tony’s, seeks to unravel the events leading up to the significant date of August 2. Tony and his sibling, Vincente Falcone, hail from humble beginnings, being the children of an Italian bricklayer. As boys, they attended school alongside Nicholas Despierre, a rather unremarkable child from the wealthiest family, and Andree Formier, a striking girl from a once grand but now declining estate. Andree’s father had perished in a concentration camp, leaving her and her mother impoverished.

By the time Tony returns to Saint Justin-du-Loup with his wife, Andree has married Nicholas and ousted her mother-in-law from the family business. The affair between Tony and Andree ignites after an encounter with a stranded Citroen, and they clandestinely meet at the blue room once a month. Despite disapproval from Vincente and his wife, the affair persists until the fateful day when Nicholas nearly discovers them.

The Tension Builds

After narrowly avoiding exposure, Tony decides to distance himself from Andree and hopes the affair will fade into oblivion. However, his sense of security is short-lived as anonymous letters begin to arrive, bearing simple yet ominous messages like, “I haven’t forgotten. I love you.”

These letters signal the onset of a more sinister series of events. Nicholas's unexpected death and subsequent exhumation reveals he was poisoned with strychnine, raising suspicions and instigating a police investigation.

Unraveling the Mystery

In December, Tony receives a cryptic note: "Happy Our Year." Tragedy strikes when his daughter Marianne finds her mother, Gisele, dying from what is later revealed to be strychnine poisoning, discovered in a half-consumed jar of plum jelly. Judge Diem presses Tony to recount the events of that day. Tony recalls accompanying Marianne to school and then visiting the village shop, where Andree, under the guise of fulfilling a request from Gisele, hands him a jar of jam which he later finds in the kitchen upon returning home to a devastating scene.

The Trial and Verdict

Throughout a lengthy imprisonment and multiple court hearings, Tony comes to realize that the village has long been aware of his affair with Andree. Despite his denials, the accumulated evidence begins to corner him. The existence of strychnine in both Tony’s shed and the Despierres’ storeroom, the postmaster's recollection of delivering the anonymous letters, and Andree’s admission to writing them all play pivotal roles in the trial.

Madame Despierre’s testimony becomes crucial in swaying the outcome. Her account reveals that Andree could not have tampered with the jam while customers were present in the shop, thus implicating Tony. Consequently, Andree is found guilty of Nicholas’s murder, while Tony is convicted for the death of his wife, Gisele. Both receive life sentences.

The novel closes on a chilling note, echoing its opening, with Andree's haunting words to Tony: “You see, Tony, we’ll never be parted now!”