This is a noir mystery set in the 1930s and involves a lesbian detective with some interesting magical skills. This book won both the Hugo and Nebula awards.
Helen made a Faustian deal and has lost her soul, as a result she has been kicked out of the magic order she and her brother were members of and is not on speaking terms with her brother.
Now her time is running out, she wants to spend it with her love, but an investigation turns into something bigger, with an unusual payoff.
This is well-written and an easy read, worth the time.