If you just want to watch an episode about Quincy solving a murder mystery, this is definitely not for you. But if you watch this show enough, and you ever wonder why Quincy is such a serial monogamist who treats every girlfriend tenderly with the disingenuous "Honey" until he leaves skid marks on his way out of their life, then watch this episode. It also explains how he went from being an ambitious surgeon to being a medical examiner.
The background is that Quincy's current girlfriend is demanding marriage - that's what you get for being late to dinner once too often! - and Quincy doesn't want to lose her, so he relents. The rest of the episode is a flashback of his marriage to his first wife - he's only had one so far - and how he felt that he let her down, with the main culprit being that he was so ambitious in his career. She didn't divorce him, she died, and that leaves her on a pedestal on top of all of the other issues he has with her memory. The odd coincidence here is that the actress playing his first wife in this episode ends up playing Quincy's actual second wife in season eight.
There is a medical murder mystery going on in the episode, but it is definitely in the background with Quincy's past being the central issue. And it is an intriguing mystery as Quincy tries to figure out how a woman who died of an overdose of barbiturates managed to have those barbiturates distributed in her body in a way that seems impossible.
They really should have given Quincy a first name at some point, just like they did with Kramer in Seinfeld. Because even his first wife is calling him Quincy in the flashbacks!