Dead Ex by Harley Jane Kozak.
Wollie Shelley's greeting card business is in limbo. She is living with her boyfriend, Simon, who is an FBI agent. An old friend (and ex-boyfriend) of Wollie's is found dead in his house, and her best friend Joey is prime suspect for the murder. Wollie knows that Joey couldn' t have done such a thing, and sets out to prove her innocence.
Wollie is a smart, resourceful protagonist, and she's very likeable. I really, really enjoyed this book (third in the series) and look forward to more.
Next up: The Ever-running Man by Marcia Muller