This 1920s scenario book MANSIONS OF MADNESS has a theme of houses (ya think?). Since the plot device is an object and not an event, it is much easier to insert these adventures into your game without outside connections; at least one, "Mr. Corbitt" (unrelated to a different Corbitt in a different house from the rulebook) has nothing to tie it down to any location. It is, in fact, in your neighborhood! Others, like "Plantation" and "Mansion of Madness" are tied to a particular region, while "The Sanatorium" is an island, but it could be off any coast. So all the scenarios are really versatile, and can be inserted into almost any campaign or even be involved tangentially in a single adventure.
The other distinguishing characteristic of MANSIONS OF MADNESS is that all of the adventures seem exciting. That's right, ALL of them. Usually you see one great, two good, and two filler. And that's a good supplement. No, all five of the scenarios in MANSIONS OF MADNESS look exciting and interesting.
"Mr. Corbitt" - a non-descript man in a non-descript house in a non-descript neighborhood. Except you happen to live there. You might think that the exotic garden he keeps in the back is the plot hook - ala "Little Shop of Horrors". If so, you'd be wrong . . . and maybe dead. As a bonus, the crypto-cultist isn't intentionally evil; he's doing the best he can in a crazy situation. One-D cultists are easy to dispose of; when the antagonist is a genuine nice guy, except for the whole "end-of-the-world" thing, it gets real interesting.
"The Plantation" There's a cult, a sacrifice, and a cultist ringleader. There's also an evil sorceress playing the cult for fools. And she's not human. And your friend (the good guy) wants to break up the cult so that he can start his own. Oh yeah, there's a GOO involved here too, but he's on your side. Of course, that's just as bad. There's some serious layers to this adventure.
"Cracked and Crook'd Manse" It's the house man, it's the house! Faster, investigators, kill! kill!
"The Sanatorium" Okay, you're on an island for rest and relaxation. Ha! Investigators only get R&R when the Keeper secretly plans to kill them all. Of course, you're trapped in an asylum on an island after a man is possessed and kills all the doctors. So now you've just got crazies walking around. What I particularly like in this adventure is that the investigators can restore order by giving medicines, continuing psychoanalysis sessions, etc. Otherwise, the crazies all become level-up POW snacks for the bad guy.
"Mansion of Madness" This is really a two part adventure, centered around a macguffin. The fun part is all the bad guys losing their humanity to possess it. This story is good and creepy in a lovecraftian way. And really, what more could you ask for?