If you're looking for a solid mystery/fantasy crossover, you could do worse than The Sword-Edged Blonde. The book started off a bit slowly for me. Maybe it was the fact that the opening violated one of Elmore Leonard's rules about beginning with the weather. Or maybe it was the fact that the first episode doesn't have much, if anything, to do with the rest of the novel. But when the story gets rolling, it works just fine.
Eddie LaCrosse has sword, will travel, but he's not eager to go to work for his former best friend, who's now a king. If he takes the job, Eddie will have to confront an unpleasant event from his past, one that he's never told the truth about to anyone. However, the king is the one person Eddie can't turn down, so he takes the case. After that, we get a mystery plot that works pretty well, a fantasy setting that's not overly heavy with magic and wizardry, the streetwise atmosphere of a good hardboiled novel with some of the trappings of noir, a narrator with an engaging voice, plenty of action, and a satisfactory resolution. Good stuff. Check it out.