The book is a biography of Harvey Milk, the first openly gay public official in the country, but there's really two parts of it: Harvey's life and the politics that he enters into in his last years. Shilts chronicles both extensively as they move along and intersect. He has excellent references and research in the book.
Harvey had a lot of lovers before and after he came out. He eventually decides that non-monogamous relationships (what we'd call polyamory) is best and lives with and loves multiple men at the same time.
What struck me the most about the book, right now, was how closely political and rights events paralleled what's happening now in elections, referendums, and activism. There are certainly good things happening now -- the states that have voted for gay marriage, Hillary Rodham Clinton's decision to give equal benefits to all diplomatic domestic partners, the way more people can be open about their lives -- but there were similar things happening in Harvey Milk's days and they were repealed and repressed.
Harvey thought all gays, lesbians, bisexuals, and transvestites should come out, "and let that world know [for] it would do more to end prejudice overnight than anybody would imagine." I can't come out because I'm not in. But I did take my Human Rights Campaign sticker out and put it on the car today. I've had it for a while and kept meaning to put it on, but didn't. So here's my step: Everybody who sees my car knows that I believe in equal rights for everybody, no matter their difference from the majority.