Captain Sonny Jennings and his core team of lifeguards monitor the dangerous Hawaiian waters; new lifeguard recruits compete to join Sonny's district; Sonny and his family grieve after the loss of his nephew; Em reveals a romantic past with Will.

When a flash flood sweeps a young tourist away from her family and out to deep sea, Sonny, Em, and Will race into action to save her. Going against Sonny's wishes, Em takes a bold risk and places her own life in danger in hopes of rescuing the lost-at-sea tourist. Meanwhile, Laka supervises rookies Kainalu and Hina's first day on the job.