After reading this for the 5th time, I finally was able to understand what was happening from the start. I'm not sure what changed between the 4th and 5th time reading it, but it just clicked this time. That said, there is no excuse a writer could give for making a story so confusing that it takes five times reading it to completely pick up what is going on. There is not enough situational context to understand cut off dialogue and thoughts and there is not enough character development to understand why characters do and say what they do and say.
**SPOILERS**
Honda saved Yoshiro and his mother from a homicidal stalker. Honda then goes on to have an affair with Yoshiro's mom, but Yoshiro is in love with Honda. Honda is then murdered. Honda's partner at the time, Asagawa, is the culprit. Asagawa was smuggling evidence and confiscated goods from police custody for the yakuza at the behest of his senior Shino-something. (The older, dark haired detective partnered with Takeda) When Asagawa fails to keep his secret from Honda and Honda notes this crime in his notebook, Asagawa is forced to kill Honda and hide his notebook. Asagawa continues committing his crime for 10 years. When his new partner discovers his secret, he must kill again. This is the opening murder.
It's not a bad plot, but the execution is poorly done. Perhaps it is really just a bad translation and when in the original Japanese the writing is easier to follow. I'm not sure, but this is a good example of why competent translation is so important. A great story can become a waste of time if the reader can't understand the words on the page.
The basic core of the plot is easy to pick up, but there is a lot of dialogue that is confusing or cut off in mid-sentence with little surrounding clues to point to what is trying to be said. This gives a feeling of being unable to connect with the character, their motives and thoughts. The translation may be poor, but I think the writing is also at fault.