Kogoro inspects the car. There are no signs of a struggle—no blood, no torn fabric. The keys are still in the ignition. In the back seat, they find a briefcase containing architectural blueprints and a lunchbox that has begun to spoil. However, something is missing: the silver locket. Yukie had specifically mentioned it, but it’s not in the car or on the ground around it.
Yukie is arrested. As she is led away, she looks at Ran and says, "Tell him... tell my husband... I’m sorry we couldn’t keep the promise of the locket." It’s unclear if she means the promise to forget the past or the promise of their marriage. Detective Conan Episode 406
Kogoro (via Conan) reveals that the locket is the key piece of evidence. It is not at the crime scene, and when the police search Yukie’s house, they will find it hidden in her jewelry box. Inside, besides Miyuki’s photo, there will be Keisuke’s fingerprints and, more importantly, traces of the sleeping pills from his system that transferred onto the locket when she removed it from his neck. Kogoro inspects the car
Initially, it looks like an accident or suicide. But Conan notices the critical contradiction: Keisuke’s watch is broken, showing the time of 2:15 PM, and the date on the watch is the day he disappeared. However, the pathologist later confirms that the time of death was around 8:00 PM that evening. If he fell at 2:15 PM, he couldn’t have died at 8:00 PM. Therefore, the watch was smashed deliberately to mislead investigators. In the back seat, they find a briefcase
The episode ends with Kogoro waking up, having no memory of the brilliant deduction. Ran is quiet, and Conan looks at a photograph of the Sonodas on their wedding day, wondering how something meant to heal could also destroy.
Yukie explains the circumstances of her husband’s disappearance. Three days ago, Keisuke left their home in the morning saying he was going to visit a construction site in the neighboring city. He took his car. He never returned, and his phone has been turned off since that afternoon. The police tracked his car’s GPS, but the signal was lost in a remote mountainous area on the outskirts of town.
She provides a photograph of her husband—a handsome man in his early thirties with a confident smile. She also mentions that he was wearing a distinctive silver locket around his neck, which he never took off. Inside the locket is a small, old photograph of a young girl, not her. When Kogoro asks about this, Yukie looks down sadly and says, "He never told me who she was. He said it was a memento of a promise he made a long time ago."