IN NUMINA: URBAN FANTASY IN ANCIENT ROME manages to shake up the formula by moving the location of the story to, well, Ancient Rome. Well, not Ancient Rome but Egretia, that is a fantasy version of the culture. That's a bit misleading from the title but that's a small issue as Assaph Mehr does his best to replicate life in the years before Julius Caesar destroyed the Republic. Or, if you're a Julian, before those dastardly traitors Brutus and Cassius destroyed the Republic. It reminds me a good deal of HBO's Rome in that there's a lot of focus on the values differences between then and now.
Felix is an occult detective working in the center of the world. A rich landlord hires him to investigate a horrific curse that has fallen over rich apartment buildings. Felix is uncomfortably saddled with his patron's daughter (that Felix states will only hurt her marriage possibilities as well as risk her life). Felix is well-versed in magic, history and detective work before the profession existed. He's aware of the supernatural but discards most surreal explanations for the mundane.
The best part of the book is the careful attention to detail that is paid in replicating not just the generic parts of Rome that people remember (aqueducts, gladiators, Senatorial intrigue) but also more daily interactions. The fact Romans had lawsuits, extensive land ordinance laws, and all the petty suburbanite adultery you'd expect. These add a lot of flavor to Felix's adventures as Egretia is both familiar as well as strange.
Felix is a decent protagonist and fun when he zigs instead of zags. Felix is a heroic figure who wants to end the curses of the apartment complexes. He's also a figure who has no problem with slavery, casual corruption, and the murder of individuals who have insulted his honor. H's also not a "good" Roman but engages in all the normal practices of a man of his station by sleeping with the wives of associates and working to benefit himself while cleaning up the city of foul sorcery.
I think readers will really enjoy this book. It's got a lot of politics, intrigue, world-building, and fun twists. This is the kind of book where the exorcism of the apartments that drive the story takes up only a third of the book followed by an extensive legal case only for things to twist against. The book sometimes overuses gratuitous but I had a lot of fun from beginning to end.