In Magic, Inc., Heinlein explores a nether world of black magic, but the pivot of the story is how legislation does, and does not, get passed. The pacing is brisk and, like many of his shorter works, would translate easily into film.
The author's portrayal of an African sorcerer would bring howls of racism today, but was, believe it or not, progressive and somewhat risky in the segregated 1940's, if only because the man is treated as an equal by all the white characters. Worth your time, and money. (I haven't read Waldo, so have nothing to add for that story.)