Hidden-away man found dead, was addicted to a fancy/medical form of opioids

Question

I read this as an English-language paperback book, bought from a discount bookstore in an Australian (likely Melbourne) shopping mall late 2019. No idea how old it was at the time. The title was bland and "literary" (as opposed to cool and spec-fic-y, the main other category of title according to my made-up rules). Unfortunetely, I have since lost track of said book.

The genre was mystery, set firmly in a city of our world. If I had to hazard a more specific guess I would say a European one. The inciting incident was when our main character (who I'm nearly certain was male) stumbles into a curious case which seems like a standard recluse (also probably male) overdosing, except that the drug in question was unusual. It was a sort of fancy medical opioid, not something that would be easy or normal to find on the street.

Investigation follows, our main character chasing leads etc. etc. though I can't remember this middle bit very well at all. He gets frustrated because while there are some interesting bits of evidence, he can't see any way to tie them together into a conclusive explanation.

At one point, close to the end I think, our main character goes to a dinner party. There's a rich guy (definitely male) who was suspected at some point, though I can't remember if he had been discarded as a person of interest. We have a scene with dramatic Revelations. Either at this point, or shortly after, our main character pieces the story together. The answer to the mystery is one of the things I remember best:

That dead guy was related to the rich guy somehow (bastard son/brother, I think) and was an embarrassment to the family. Therefore, he had to be hidden away. He was provided with a small apartment for himself, which he decorated with tiny figurines, though not much else. These figurines had been seen by the main character when he searched the apartment during the investigation scenes, who remarked on them - they contributed to the oddity somehow, though I can't remember why.

Anyways, to keep the bastard hidden, he was additionally given an endless supply of drugs to occupy his time. The rich guy varied the drugs sometimes, just for kicks. That's how the fancy medical drug made its way into the dead guy's body. Eventually, the rich guy has the dead guy killed; he justifies this at one point by saying it wasn't much of a life to be living.

I am nearly certain at least one of the dead guy, rich guy, or protag was homosexual. If they weren't, then a side character probably was. My brain has this book firmly shelved in its "secretly gay novels" section, though it refuses to explain why.

What novel was this?

Answer 1

A Chemical Prison, by Barbara Nadel

I found the book after doing a major cleaning of the bookshelf at my parent's home. Seems I got various minor details wrong but the core idea (keeping a kid prisoner via addictive drugs) was remembered correctly.

The book is set in Istanbul, Turkey. While the dead man was 'a user of hard drugs' (ch. 2, pg. 14), he does not appear to have overdosed:

Gently but firmly, the doctor pushed the young man's head to one side, revealing to Ikmen's gaze a dark purple and red line around the base of the throat. 'I would say that he was strangled, possibly by ligature,' he said, 'which, if I am right, opens the door quite neatly to some very foul play indeed.'
_{ch. 2, pg. 15}

The apartment lacks 'personal touches' (ch. 2, pg. 15) except for the figurines:

on top of the chest of drawers [were] little crystal figures, about fifty of them, all arranged in neat rows across the top of the chest; animal, domestic items, little people, tiny houses, palaces, mosques. Each in its own way a dazzling work of art and, making up a collection of such magnitude, probably worth quite a lot of money too.
_{ch. 2, pg. 15}

These contribute to the contradictions present: the man appears to have been imprisoned in an attic area, given fancy things (the figurines), kept addicted since childhood, but not used as a sex slave (the first explanation reached for). The rest of the apartment is very clean and, according to the landlord, rented to a quiet and well-behaved foreigner. Then there's the question of the drug found in the dead man's system, which was indeed medical:

Look, pethidine is a synthetic form of heroin. Its principal use is in the alleviation of pain during childbirth. Like any drug, it possess the potential for abuse but as an actual street drug ... I have never heard of or experienced it being used as such. Some medics have been known to "experiment" with it, but beyond the medical sphere it is, I would say, really rather difficult to obtain.
_{ch. 7, pg. 114}

The book establishes that the man couldn't have stolen it from the workplace because his hands are too soft; he has clearly never worked in the medical field as then he "could not have had atrophied limbs or hands that were soft and unused." (ch. 7, pg. 115)

Ikmen does attend a dinner with Ersoy (the man who orchestrated the whole plan), but that is in the middle. Everything is revealed when Ersoy infodumps at Ikmen. It turns out that Ersoy was a disappointment to his father for being gay, and thus a new wife and child were procured. Ersoy arranged for the death of his father and would have killed the new son but for his lover Avedykian. Avedykian was a doctor and the source of the drugs which kept the kid docile. The drugs did vary based on what Avedykian could easily obtain. Eventually Ersoy killed the new son anyways out of "envy" for his youthful appearance, not because it wasn't a life worth living.