The protagonist of David Levithan's Every Day, A, is a different person every day. A doesn't have a family, friends, a gender, a home body, or a name beyond that initial. What A does have are rules: not to vastly change the host's life, not to let the host's first experience of something (sex, for example) happen while A is inhabiting his or her body. A travels only among the bodies of people A's own age. As Every Day opens, that age is sixteen, but after 5,993 days of body-hopping, A is a very mature, very aware sixteen.

Which makes it easy, when A wakes up in the body of a boy named Justin on day 5,994, for A to see that Justin's girlfriend, Rhiannon, wants something from Justin that he isn't giving: "I know from experience that beneath every peripheral girl is a central truth. She's hiding hers away, but at the same time she wants me to see it. That is, she wants Justin to see it. And it's there, just out of my reach. A sound waiting to be a word" (p. 5). Despite a determination not to get involved in hosts' lives, A wants to hear that sound become a word. The two cut class to drive to the ocean—without Rhiannon knowing, of course, that she's with A rather than Justin. During their afternoon, the two trade songs and truths, and A is in love. Suddenly, it isn't so easy to move without ties into day 5,995.

Rhiannon ends the day at the beach with no idea, still, that A is someone different from Justin, but that doesn't stop A from plotting ways to see her and attempt to connect with her in several different bodies. Instead of "accessing" hosts' memories to learn and copy their daily routines, A maps out the route to Rhiannon's school from the next several hosts' homes. A shows up with stories that will allow A to spend time with Rhiannon—on day 5,997, A drives Amy Tran's body from her house to Rhiannon's school and poses as a potential new student in need of a tour guide. A few days later, A drives host Nathan Daldry to a party where A expects to see Rhiannon.

In each body, A is striving to recreate that sense of connection with her that A felt during their day at the beach. A wants Rhiannon to see, without prompting, the essential A inside of each host body. Eventually—after Rhiannon spots the holes in A's cover story for Nathan's presence at that party—A tells her the whole truth. That's when A's struggle to get Rhiannon to see, and love, A the consciousness truly begins. Even once Rhiannon is convinced that A's story of hopping bodies is true, she has a hard time loving A while leaving physical appearance out of it. Rhiannon is less touchy-feely with A when A shows up in a girl's body; she "can't see [A] inside" (p. 274) when A comes to meet her in the body of a 300-pound boy, either. And while meeting Rhiannon expands A's world, their relationship contracts hers. Because A's situation is impossible to explain, Rhiannon is left to choose between A and her longtime friends.

Levithan has addressed the idea of love without gender specifics before, in The Lover's Dictionary (2011), which tells one unidentified couple's story only in dictionary entries. Every Day takes this scenario a step further. The entire book is a fascinating, important thought experiment (and, happily, Levithan's writing is also lovely). But it's an experiment that goes much more successfully for A, who already sees beyond any kind of gender binary, than for Rhiannon. That makes Rhiannon a useful proxy for the reader who lacks A's life experience and awareness. (After meeting A as a boy in Justin's body, I certainly struggled not to think of A as a boy for the rest of the book, and I caught myself using masculine pronouns several times while writing this review. Even the flap copy makes one use of "he.")

Rhiannon also works as a stand-in for the reader because her personality only comes through in flashes—her kindness to Amy Tran, her enthusiasm while dancing with Nathan, the occasional quip when she and A are together in a coffee shop. Sometimes I wanted to see more of Rhiannon and her evolving feelings toward A, but mostly I was satisfied and engaged by A's own story.

A's ability to get inside so many other people's heads makes A an ideal writer's character. A's range of experience also makes the occasional broad pronouncement about humanity seem natural rather than annoying: "Everybody wants to belong to something bigger than themselves, and everybody wants company in doing that," A notes at one point while in a host body on the way to church. "They want there to be a force of good on earth, and they want an incentive to be a part of that force. . . . They want to touch the enormity" (p. 77).

After years of hopping from one body to another, A understands well the two poles of human experience—the individual and the enormity—but very little about the vast space in between where complicated individuals try to form relationships. Spending time in that space with Rhiannon changes A, opening A up to the idea that A doesn't have to move from body to body with no impact on the host. A's presence in a body for a day can be enough to change a person's life for the better, if A chooses to get involved. For A, growth involves not becoming more aware of the larger world, but more willing to be present in the smaller one, even if only for a day.

Sara Polsky (http://www.sarapolsky.com) is a writer living in New York City. Her first novel, This Is How I Find Her, will be published by Albert Whitman in fall 2013.