The Mystery Gang goes to Hawaii for the Big Kahuna of Hanahuna Surfing Contest. However, the gang and the locals find the island invaded by the vengeful Wiki Tiki spirit and his demons.
When Daphne is given the opportunity to design clothes for a company in Hawaii, the entire gang travels along with her. As they are leaving for their destination, a man warns them that there are evil spirits on the island, but the gang is doubtful. When they arrive in Hanahuna, they are excited to watch the Big Kahuna of Hanahuna Surfing Contest, which Manu (a local) had won previously. Because the Mayor of the area welcomed everyone including mainlanders to the Surfing Contest, the Wiki Tiki spirit was angered. The gang and everyone in the area are threatened by the demons of the evil Wiki Tiki who also have kidnapped Manu's beautiful girlfriend Snookie.—katie
A surf and beachwear company named "Goha Aloha" offers Mystery Inc. a complimentary trip to Hawaii in exchange for Daphne Blake creating new swimwear for them. The group meets with Jared Moon, a Goha Aloha representative, when they arrive and finds out about the Big Kahuna of Hanahuna surfing competition. Originally reserved for native islanders, the mayor opened it to mainlands after protests from a number of islanders, including local surfer Manu Tuiama and his best friend Little Jim. The former is particularly agitated about this because he believes that local real estate agent Ruben Laluna constructed a residential complex on sacred land, and that the ancient Wiki-Tiki spirit sent demons to attack his village and abduct his girlfriend Snookie in retaliation for the mayor's actions.
Manu and the gang visit Auntie Mahina, a local shaman who lives deep in the jungle, while looking into the attacks; however, it appears that the Wiki-Tiki kidnaps Manu in the process. Before instructing the group to go to a nearby volcano or risk Manu and Snookie being sacrificed to the monster, Mahina explains that the Wiki-Tiki is upset because the surfing competition is a Hawaiian custom and the winner must be of Hawaiian ancestry. Mahina gives Fred Jones a necklace made of bola Gawain root extract before they depart, claiming it will protect him from the Wiki-Tiki. When the group finally makes it to the volcano, they locate Snookie, but the Wiki-Tiki captures her again because she is impervious to the necklace.
The group finds out that the Wiki-Tiki's demons are remote-controlled robots and a photo of the Wiki-Tiki herself riding a surfboard made by the Goha Aloha brand after they have escaped. To entice the monster, Daphne competes in the surfing competition the following day. She eventually overcomes it with the assistance of Shaggy Rogers and Scooby-Doo, enabling the others to expose it as Manu, who they disclose collaborated with Snookie to frighten away residents and visitors in order to purchase their houses and resell them for more money. To further their plan, Snookie, a master of robotics and rocket science, built and controlled the robots. Scooby's efforts to stop Manu before the gang celebrates at a luau earn him the title of Hanahuna's new Big Kahuna as the criminals are taken into custody.
