From Wikipedia:Cast a Deadly Spell (1991) is a Horror/Detective HBO movie with Fred Ward, Julianne Moore and Clancy Brown. Ward stars as 1940's hardboiled private detective Phillip Lovecraft, in fictional universe in which magic is real, monsters and mythical beasts stalk the back alleys, zombies are used as cheap labor, and everyone -- except Lovecraft -- uses magic every day. Yet, cars, telephones and other modern technology also exist in this world.
The movie is very much an homage to the works of H. P. Lovecraft. Though not based on any one particular story by Lovecraft, the film features many Lovecraftian tropes, and can be considered to take place against the unified backdrop which has come to be known as the Cthulhu Mythos. Frequent references are made to the Necronomicon, the Old Ones, and Yog Sothoth throughout the film.