"Vida" by Marge Piercy

Most fiction about activists makes me cringe, but Piercy's characters here are naive only because it's the 1970s, and she avoids reducing any of them to caricatures. The personal and the political are not just juxtaposed to prove a point but are completely interwoven, and give someone my age a much-needed insight into the roots of feminism and sexual politics. It also keeps you guessing until the end, which gives any book that essential compulsive quality. Seems to be out of print, but there are plenty of copies on Abebooks.