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.

Em works to earn the team's respect when she is left in charge and Hina and Kainalu juggle multiple beachside emergencies. Meanwhile, Will's fiancé pays him a visit at work, Sonny opens up to a former lifeguard about his trauma since losing his nephew, and Laka continues his flirtation with EMT Jenn.

A morning hangout on the beach almost turns deadly for a group of college kids when two of them get trapped in a collapsed sandpit. Meanwhile at sea, Sonny, Will, and Laka race to rescue people stranded after a shark attack. During a rescue, Em catches the attention of Fire Captain Sean Harimoto, and Will learns if he made the cut for the firefighter job he has been pursuing. Hina makes a move with Kainalu, and Sonny attends Zion's memorial fundraiser and attempts to reconnect with his sister for the first time since the funeral

The lifeguards of the North Shore experience the most dangerous ocean conditions the district has seen in years. Sonny assigns Laka as acting lieutenant as Em has the day off and joins Jenn to catch some massive waves. Meanwhile, Kainalu's father pressures him to leave his shift and help him with his campaign over patrolling the beaches. Hina thinks she is ready to back-up the rescue skis, and Laka and Will almost make it through the day when a fight breaks out among locals. Emotions reach a boiling point for Sonny when he experiences another loss.

The North Shore community comes together for Rocky's paddle out; Hina thinks about switching districts; Laka, Will and Kainalu try to save a beachgoer that accidentally speared his own foot; romance heats up between Sean and Em.

An influencer gets swept into the ocean while trying to film a new video; Kainalu and Hina discuss setting boundaries within their home; Mayor Emerson makes good on his word with Captain Sonny; Jenn finally agrees to go on a date with Laka.

Sonny, Em, Will and Laka look for missing paragliders that were pushed into the ocean by a down draft; Kainalu invites Hina to a party with his ex-girlfriend; Jenn doesn't think Laka is serious enough for her; Sonny puts in his notice to retire.

Christmas cheer is in the air as the lifeguards prepare for their annual holiday toy drive; while surfing, a local grandpa has a heart attack and is rushed to the hospital; Sonny tells Laka he is not ready to become a lieutenant.