Cassy lost her memory. Until Mikael shows up with her and pretends to be a stranger. And then a few years later, she gradually remembered what her connection to Mikael.
She was the competitive gymnast who felt like no one loved her. He was the baseball player who had loved her for a while. When these two high school seniors get together, life changes in ways they never would have expected.
I suck at summaries, so don't judge the story based on this.