Invisible helix

The body of a young man is found floating in Tokyo Bay. But his death was no accident - Ryota Uetsuji was shot. He'd been reported missing the week before by his live-in girlfriend Sonoka Shimauchi, but when detectives from the Homicide Squad go to interview her, she is nowhere to be found. She's taken time off from work, clothes and effects are missing from the apartment she shared. And when the detectives learn that she was the victim of domestic abuse, they presume that she was the killer. But her alibi is airtight - she was hours away in Kyoto when Ryota disappeared, forcing Detectives Kusanagi and Utsumi to restart their investigation. If Sonoko didn't kill her abusive lover, then who did?