May I touch your cape?
For a lighter read, try the Rivers of London series by Ben Aaronovich. Murder, mystery, and magic. Think Dixon of Dock Green (or Morse) meets Harry Potter.
If you “love Stephen King”, you should at least like F. Paul Wilson very much.
Unlike a lot of authors, Wilson is a real genre-hopper. But his best work is probably the “Repairman Jack” series. Start with “The Tomb”. (The series is complete so you don’t have to worry about missing the end.) If you like, keep going. If not, well, he’s also done SF, Cook-like medical thrillers (Wilson is a practicing physician.) And a few others that don’t neatly fit particular categories.
Another author just occurred to me: Graham Masterton. Much like Stephen King, his books start really strong but frequently fall apart toward the end. I was only able to find a couple of his books back when I was searching for Kindle versions, so I don’t have a very broad command of his work. Still, I’d recommend Ritual, which is about as stomach-turning as it gets, until it reaches the rather ridiculous ending. Plague also started strong, looking like it would be as epic as The Stand, but then it seems like Masterton only had a couple of days to wrap it up or something, because the last third or so seems really rushed.
Lars Kepler: The Norwegiean Serial-Killer Type
James Rollins: Less douche-y Dan Brown
Boris Starling: Specifically Messiah, fantastic murder mystery novel
If you can find a copy, check out “The List of Seven” by Mark Frost (the co-creator of “Twin Peaks” with David Lynch). It’s been a few years since I read it but I believe it checks off all the boxes specified by the OP. It’s a Victorian era mystery/thriller with a good chunk of horror mixed in. The protagonist is a pre-Holmes Arthur Conan Doyle working alongside a character who would obviously become his model for Holmes later on.
Tim Powers is awfully good in the realm of fantasy/suspense. He’s most famous for his first novel, The Anubis Gates, a time-travel literary story which I admire but which bugged me in several ways (the protagonists keep jumping into the Thames River in the 1820s like it’s a chlorinated swimming pool rather than an urban flow of literal shit and piss).
His second book, Last Call, a contemporary novel of Tarot magic, chaos science, competitive poker, and T.S. Eliot’s “The Waste Land,” is flawless. Give it a go.
Trevanian The Eiger Sanction.
My Horrific Horror Fic Picks:
David J. Schow, Jack Ketchum, and **Richard Christian Matheson
** are all good for some excellent, icy short stories.
John Farris has written several above-average horror novels, of which All Heads Turn When The Hunt Goes By is by far the best and scariest.
John Shirley is mostly famed as an SF writer, but he’s written some out-there horror, too; mainly in his short stories and the two short novels that make up Demons
The Amulet, Cold Moon Over Babylon, and Katie are classic 1980s pulp-horror by Michael McDowell. The first two are set in the present-day Deep South, while Katie is historical horror set in 1890s New York City. They’re all fun, bloody reads with creepy atmosphere, bone-crunching violence, and a sly malevolent humor.
*Falling Angel *by **William Hjortsberg **, is even better than the movie based on it, Angel Heart. It slowly builds up to a clammy, queasy dread that’s hard to shake even after you’re through with it.
And, of course, there’s anything by Joe R. Lansdale.
Elizabeth Engstrom’s When Darkness Loves Us is two separate short novels, the title piece and Beauty Is. They’re a different kind of horror, both brutal and emotionally moving at the same time.