After being thought dead at the end of the tenth season, Mitch Buchannon [David Hasselhoff] is revealed to have only amnesia, recovering in a Los Angeles hospital and having retired from Lifeguard duty. His new fiancée, Allison Ford [Alexandra Paul], resembles his old lover, Lt. Stephanie Holden [Alexandra Paul], who died during the seventh season. This uncanny resemblance stirs a mix of nostalgia and tension as Mitch and Allison begin to carve out a new life together.
Taylor Walsh [Angelica Bridges] now runs the Baywatch Headquarters, where Leigh Dyer [Brande Roderick] and JD Darius [Michael Bergin] are in a relationship, and Mitch's son Hobie [Jeremy Jackson] has started a relationship with Summer Quinn [Nicole Eggert]. Taylor manages to lure Mitch back to Baywatch to introduce everybody to Allison, and they’re all surprised by how closely Allison resembles Stephanie Holden, a revelation that disturbs Mitch’s ex Neely Capshaw [Gena Lee Nolin], who shows up hoping to win Mitch back and becomes suspicious of Allison.
Meanwhile, C.J. Parker [Pamela Anderson] is opening a bar and grill in Hawaii and invites many of the old lifeguards from Baywatch there for a reunion, including Caroline Holden [Yasmine Bleeth], now an actress. Also there are John D. Cort [John Allen Nelson] and Eddie Kramer [Billy Warlock], who starts a relationship with Caroline after being separated from Shauni. Lani McKenzie [Carmen Electra] is now a Hula Dancer and is good friends with C.J. Kekoa Tanaka [Stacy Kamano] and Jason Ioane [Jason Momoa] are now in a relationship. C.J. gets a call from Mitch to announce his engagement to Allison and to tell her that they booked their wedding in Hawaii. But while everyone’s there, Mitch’s old nemesis, Mason Sato [Cary-Hiroyuki Tagawa], takes pictures of his loved ones to plot his revenge against him.
Neely, still suspicious of Allison, gets into a fight with her in the water, in which she discovers her fingerprints on a necklace, which she gives to Jason Momoa to give to his detective brother to run a check on her. After they have the engagement party, they take a boat to Haiku Island, where the wedding will take place.
When they arrive there, Sato’s men prepare to capture and drown Lani, Cort, Eddie, Caroline, Hobie, and Summer and record it all on video. Also, Neely finds out from Kekoa and Jason that Allison is really Judy Radin who served time for forgery and assault with a deadly weapon, and had reconstructive surgery done to look like Stephanie, but Mitch doesn’t believe her until he confronts Allison, who reveals her partner: Sato. Neely and Mitch go to save Hobie and Summer, Leigh goes to save Cort and Lani, and J.D. goes to save Eddie and Caroline. But after Mitch and Sato fight, Neely punches Allison and takes the gun from her.
Eddie, Caroline, Lani, and Cort get rescued, while Mitch and Sato continue their fight on the rescue boat, and Sato is killed by the propellers of the boat underwater. The Coast Guard arrives to arrest Allison and Sato’s henchmen, and Mitch breaks off their engagement. J.D. and Kekoa became lovers again, and as did Jason and Leigh.
C.J. and her co-worker Lorenzo [Jason New] decide to get married so there would be a wedding while everyone watches, and Mitch and Neely reconcile as well.
