We're not gonna lie: it's tricky to summarize a novel's plot when the thing has four intersecting timelines—even trickier than rocking a rhyme that's right on time (it's tricky). But we'll give it a shot for you, dear Shmooper.
We open (more or less) in Manhattan, 1969. A woman named Joanna is intrigued by the headlines she's seen recently: it seems that Earth has a visitor from a planet run entirely by women. Joanna doesn't own a TV, so she heads to a cocktail lounge where she can watch a live interview with the blonde, attractive lady alien, whose name is Janet Evason Belin.
As she sits in the lounge, Joanna notices another woman there who seems slightly younger than her, and whose clothes are totally out of date. That's Jeannine. She's from… away. Jeannine has no idea why she's suddenly sitting in a cocktail lounge in Joanna's world, but pretty soon she pops out of existence again, so… yeah, no harm, no foul.
Joanna wants to hear everything she can about this Janet from another planet, and over the next month or so she follows all of the media stories covering the Whileawayan emissary's visit. For some reason, Jeannine keeps popping up in Joanna's house, running through walls and getting stuck in mirrors. Joanna figures the world is a strange place, and decides not to worry about it.
Finally, one night while Joanna is standing on Broadway and watching a parade, Janet pulls up in a limousine and invites her in. Jeannine's there too (why, we don't know), and the three J's go on a little joyride.
For six and a half months, Joanna lives with Janet in a large hotel suite and shows her around Manhattan. Jeannine flits in and out of the picture too, and sometimes Janet kicks her. Joanna tries to teach Janet the ins and outs of North American culture, and she tries her best to make the alien woman act like a lady. Janet, for her part, struggles to understand the gender roles that govern Joanna's world.
At a party on Riverside Drive, Janet gets roped into conversations with men who have strong (and not so nice) opinions about the new feminist movement, and about women's incompetence in general. When she and Joanna try to leave, the guy hosting the party assaults them, and Janet beats him up.
Eventually, Janet and Joanna move out of the hotel suite and into the home of an all-American family in Anytown, U.S.A. Janet attends women's luncheons and school fairs, and Joanna hovers around the house like a ghost. Jeannine pops in and out too, like she does. The family's teenage daughter, Laura Rose Wilding, begins to fall in love with their alien guest, and one evening when her parents are out, she and Janet go to bed together.
Here's where things get tricky (we know what you're saying: here is where they're tricky??):
At some point during all of this, Joanna and Jeannine find themselves in Whileaway with Janet. Then, at some point after all of that, Joanna and Janet find themselves in Jeannine's world. There, Jeannine spends a lot of time agonizing about the fact that she's twenty-nine years old and still not married. She's got a boyfriend named Cal, whom she doesn't really like, and a family who keeps nagging her to get on with the whole marriage and babies thing.
During a summer vacation in the Poconos with her brother, his wife and children, and her mother, Jeannine is urged to date around a little so that someone might finally ask to marry her. Eventually, she gives in and telephones ho-hum Cal to come and bring her home, and the two get engaged.
Back in Joanna's world—where Janet and Laura are seeing each other pretty regularly and Jeannine is still doing that thing where she runs in and out of walls—the three J's are getting along okay. Suddenly, they find themselves in a place that none of them has ever seen before: an ultra-modern apartment that seems to be overlooking the East River. There to greet them is a woman named Jael, who explains to them that all of this world-hopping is actually her doing. In her world, probability travel is a fairly new invention (and a pricey one at that), and she's been trying to bring all four of them together for quite some time.
Janet, Jeannine, Joanna, and Jael: suddenly it's clear that all four women are essentially the same person, distinguished only by the unique circumstances that have shaped their lives in their own homeworlds. In Jael's world, women and men have been at war for about forty years—a war that's left Europe looking as pockmarked and scarred as it did after World Wars I and II in Joanna's world (and, you know, ours).
Jael takes the other three J's through the underground cities inhabited by women, and brings them along on a business trip to Manland. The business meeting takes a turn for the worse when Jael assassinates the Boss she was talking to, and the other three J's start to have some doubts about her reliability. After spiriting Janet, Jeannine, and Joanna away to her home in Vermont, Jael tells them why she's brought them all together. What she wants is their support in her war.
The novel ends back in Joanna's world, as Janet, Jeannine, Joanna, Jael, and the novel's omniscient narrator get together for a Thanksgiving dinner at Schrafft's. When Jael repeats her request for support, Jeannine agrees, Janet declines, and Joanna doesn't answer the question. As the women part ways, the narrator bids farewell to The Female Man, and sends it out into the world.