After being jailed for solving another mystery, the Mystery Inc. gang stumbles upon another mystery: a gruesome monster lurking underneath the town and cocooning everyone who comes near in green goop.

Strange things continue happening in Crystal Cove, when doorknobs suddenly vanish and a priceless diamond is hidden somewhere. To top it all off, a mysterious Ghost Trucker is also scaring the town.

A Man Crab attacks Crystal Cove beach during a volleyball tournament for Trickell's Triquid diet mixture. The gang must stop him and solve this mystery before the tournament's female players, who the Man Crab has taken a liking to, are put in danger. Meanwhile, Velma gets some relationship advice from Daphne.

When two giant monsters start to attack Crystal Cove, Mayor Jones asks Fred and the gang to help him and the sheriff capture them. Meanwhile, Shaggy has to choose between his relationship with Velma and his friendship with Scooby.

When Fred invites the gang on his and Daphne's second date, it pushes Daphne into the arms of Obnarb, the leader of an Orc Biker group called the Wild Brood who have come into town. When a break in at the armory happens and a dangerous weapon is stolen, the Wild Brood are the top suspects. It's up to the gang to solve this mystery, save the Wild Brood, and find the imposter Orc Biker.