Anna Fitzgerald's sister, Kate, is dying of leukemia and needs a kidney. Anna is expected to give her one, but Anna is sick of giving things to her sister. (Not just toys and money, but blood and plasma.) See, Anna was genetically engineered to be a donor for her sister Kate, but she doesn't want to do it anymore; Anna wants to choose what she gets to do with her own body.
Thirteen-year-old Anna hires Campbell Alexander, an attorney, to sue her parents for medical emancipation. Campbell has a crazy family life of his own, so he agrees to help her. Needless to say, this doesn't go well with Sara, Anna's mother, who gets served court papers while waiting beside Kate in her hospital bed. Brian, Anna's father, kind of agrees that Anna should have the right choose, which only makes Sara mad at him, too.
A woman named Julia Romano is designated as Anna's guardian ad litem, a woman who will work with Anna to try to decide what is best for her. (In other words, someone who will make the decision for Anna in a case that is to determine whether or not Anna can make decisions on her own—say that five times fast.) And, what a co-inky-dink, Julia and Campbell were lovers in college, before he dumped her without warning.
Over the course of a week, Anna waffles back and forth between wanting to give Kate a kidney and wanting to keep her own kidney and watch her sister die. Julia and Campbell sleep together again. Sara decides to represent herself in court, and Brian moves into the fire station where he works and takes Anna with him. And, oh yeah, the Fitzgeralds' son, Jesse, turns out to be an arsonist. Sorry, Jesse, we almost forgot about you… just like your parents did.
In the end, the judge awards Anna medical emancipation. It turns out that Kate wants to die because she's sick of living with cancer anyway, and the whole lawsuit was her idea the whole time. (So much for Anna's choice, huh?) Brian stops Jesse from being an arsonist; Campbell reveals to Julia that he broke up with her because he has epileptic seizures (Julie's and our reaction are similar: Seriously, dude?); and Brian and Sara reconcile.
And everyone lives happily ever after.
Well, until Anna suddenly dies in a car accident literally right after the trial. Because Campbell was awarded power of attorney, he says that Anna's kidney should go to Kate. Kate survives the transplant and lives, even though her sister dies. Brian and Sara regret neglecting Kate her whole life, and Kate lives with the memory (and the kidney) of her sister.