Tippi and Grace. Grace and Tippi. For them, it's normal to step into the same skirt. To hook their arms around each other for balance. To fall asleep listening to the other breathing. To share. And to keep some things private. The two sixteen-year-old girls have two heads, two hearts, and each has two arms, but at the belly, they join. And they are happy, never wanting to risk the dangerous separation surgery. But the girls' body is beginning to fight against them. And soon they will have to face the impossible choice they have been avoiding for their entire lives.