Becca Wong Walker may be so shy that most people at school think she doesn't speak at all, but why should she care? She has more important things to worry about. Missy, the manatee who visits the dock in Becca's backyard, and Becca's only friend, hasn't been seen for a long time. When Missy finally does return, she has a new baby with her! Becca wants to be excited, but more than ever inconsiderate boaters are speeding through the river, putting the lives of Missy and her baby in terrible danger.

One day, Becca spots a dolphin in the river too! By bonding over the dolphin and manatees, Becca finally starts to make friends at school. But when Becca takes a video that goes viral, it seems like it will be harder than ever to save the manatees... and trying might just tear Becca's new friendships apart.