Well, episode 536 is an anime original, since I don't remember reading it in the manga. And it's a one episode case, the way most Conan originals seem to be. As far as timeline goes, it could almost be placed anywhere, if not for a new character (who first appeared in ep 509) mentioned by Haibara.
Spoilers, well, up to about half of the episode, I think.
So there is this reclusive, unfriendly middle age man who takes up residence in a reputedly haunted mansion for some unknown reason. Being little busybodies, Conan and the detective boys decide to go scouting/investigating the house. (Well, just the detective boys decide; Conan is there to keep an eye on them and Haibara is probably there to keep an eye on Conan.) When they arrive, they find the aforementioned man is having a dispute with a guy who sounds rather whinny to my ears. The whinny guy leaves after he unsuccessfully tried to pursuade the mansion owner (MO) of something.
Enter the kids, who turn craven when the MO demands what they want with him. Conan, however, notices the nameplate is missing a name and asks MO about it. MO says he cannot put anything on it yet, and goes back inside, to the kids' consternations. (The MO is not being particularly nice.)
Fast forward to the next day, Genta relates to the rest of the group that the MO is dead. It seemed he passed away in the middle of the night. The kids, of course, can't let the matter rest (in fact, Conan says that himself), so they return to the mansion again. There, they find a man and a woman who appear to be connected to the dead MO. The man introduces himself as an art dealer and the woman as his secretary/assistant. He says the MO is a famous Western-style painter and he is here to look for MO's last masterpiece.
Oh, the whinny guy shows up again, and has a bad manner to say 'lucky' after hearing about the MO's passing. Turns out the argument he had with MO was he wanted to demolish the mansion and wanted MO to move out (MO made a deal to rent the mansion for three months, and that time period was up already), but the MO asked for a little more time (2-3 days). Anyway, I think the whinny guy totally deserves what he gets during the course of this episode.
I don't want to give the main twist away, though, so I'll stop here. That said, 536 is not a deep mysterious case or even the one of the best Conan chapters/episodes, but it works on me on a sentimental level (even if I'm not sure if that is very realistic).