Can you use astrology to fight crime? The answer is yes! San Francisco astrologer Julia Bonatti gets involved in a suspicious death at a long-time client's family home, and the intrigue deepens when the client's elderly aunt falls in with a cult that has it in for the occult.
Bonatti figures out that the elderly aunt is in danger because her Mercury or whatever planet transit doesn't look good. The detective work isn't all astrology, it's a lot of regular sleuthing--sticking her nose in everywhere and putting herself in harm's way more than once. It's very San Francisco, though people of younger generations than the author may be uncomfortable with di Marco's not totally up-to-date framings of alternative cultures. It's also weird that Bonatti doesn't use her cell phone all the time and has an answering machine.