I'm writing a crime/mystery fiction novel.
The main plot involves a murder at the start, a case that my protagonist, a police detective, has to solve. He faces conflict and difficulties along the way, until solving who did it and making an arrest. At the inciting incident, he discovers that the homicide victim (who was a family friend) had in his possession an item that belonged to the detective's wife, who mysteriously died five years earlier.
Running alongside this main plot is the subplot linked to his wife. This subplot influences his character arc through the story. His wife was presumed to have drowned five years earlier, and after several years missing, 'death in absentia' was declared for her. He refuses to accept her death, as a body was never found. Relations had been excellent between them, though, and he knows she wouldn't have voluntarily disappeared like that. With her case unsolved, it went cold. The last person with her on the day she disappeared was the family friend, the new homicide victim. The detective always believed the family friend had something to do with her disappearance, but there was no proof, no evidence linking him to her death. The item found on the new victim forces the detective to reinvestigate her case alongside that case.
For the detective, solving his wife's disappearance (subplot?) has higher importance than the current case as it would allow him some closure and a chance to move on with his life. The homicide of family friend, however, is the main plot running from the beginning to the end and, I think I'm right in saying, would typically be assigned to the following plot points:
Inciting Incident / First Plot Point / First Pinch Point / Mid-Point / Second Pinch Point / Third Plot Point / Climatic Moment / Resolution
The hook at the beginning will be the homicide of the family friend.
Although the events of his wife's death happened as backstory, with my Protagonist having such a strong connection to this subplot, I'm wondering if I should assign that to these plot beats/points instead and using that as the force driving him forward at each stage?
Thank you in advance for your answers.