Teddy used to love lifeguarding Bottomrock Lake, until her twin went for a midnight swim and never came back. Being a talented swimmer, Izzy couldn't have drowned. If she did drown, where is her body, why is her passport missing? Then Toby, who watched Izzy disappear, takes a job as a lifeguard. With Toby's help, Teddy will spend one final summer trying to figure out what happened to Izzy.