Peter and his best friend, Tommy, have a goal for their last summer before middle school: finish their Discovery Journal, a catalog of the wildlife around their Florida town. When they spot a manatee in a canal, Peter knows they've found something special--and when the manatee is injured by a boat, something to protect!

As Peter joins the fight to save Florida manatees, he also finds himself taking care of his ailing grandfather and facing an unwelcome surprise that jeopardizes his friendship with Tommy. Soon Peter is adrift, navigating shifting tides and realizing that he has as much to discover about himself as he does about the world around him.