I picked up Van Richten's Guide to Ravenloft and have been reading it cover to cover. This is my review of the book, chapter by chapter. Chapter 3 covers over 30 domains, so I'm posting about it as I work my way through the different domains.
Mordent is a hanted domain, and the horror genre listed for it at the start of the section is ghost stories. Personal drama is high in the Mordent backstory, although much of it is subdued in the 5e version. In the 5e version of Mordent, the ghost of one Lord Godefroy is the darklord of the domain, and he's tormented nightly by the unrestful spirits of his daughter and wife, both of whom he murdered one fateful night in the House of Gryphon Hill.
Not only was Lord Godefroy a murderer in life, he was an extortionist after death. For fear of being discovered, he blackmailed Daniel Foxgrove into spying on the townsfolk to ensure they weren't deducing Godefroy's evildoings. Foxgrove is the father of none other than Laurie and Gennifer Weathermay-Foxgrove, whose correspondence with Van Richten was referenced in the book's introduction. In fact, Van Richten owns and runs an herbalist shoppe in Mordentshire, and when he's away (presumably hunting monsters), Laurie and Gennifer would tend to it.
There isn't a strong plot for Mordent, but as usual there's a plot table to give you some ideas. According to the domain's theme, though, the implication is that you're meant to run a story featuring ghosts, and so there are several tables to help you build a ghost with an interesting backstory. The ghost tables and the plot table don't necessarily always align (one plot hook is the investigation of a giant raven terrorizing a village, for instance) but you could probably either combine the plot hook with a ghost subplot or else just use the motivations and backstory you build with the tables for whatever enemy you end up using.
Mordent is one of the earliest domains in Ravenloft lore, having been introduced in the second-ever Ravenloft module. There's nothing particularly unique about it except that it's a spooky place that's home to more than its fair share of annoyed poltergeist. Its main attraction, I think, is the House on Gryphon Hill. There's considerable nuance to the house, because it's the house that knows of Godefroy's murders, making it conceivably an ally. However, Godefroy currently inhabits the house still, and he's got a staff of servant spirits whom he lords over with the threat of severe punishment by his spectral hounds. So the house could feasibly used as a haunted house in an adventure, or player characters could be called in to rescue the house and the spirits inside of it (with maybe some loyalist spirits presenting the usual threats.) Or, obviously, you could just reimagine the lore a little and make the house complicit in Godefroy's bad behaviour.
Mordent is an easy setting for a supernatural story, which is isn't saying much because there are few D&D settings that aren't. But if you're setting a mood, Mordent might have that baked in already, making it an easy location to adopt. This book is pretty light on the details, but if you can find a copy of the 3.5 Ravenloft Gazeteer 3, then you'll find about 50 pages of setting description and lore (and very little of it is affected by this 5e update.)