Brothers Johnny and Scotty have a summer of fun and sun in store for them as they visit their Aunt Maxine and cousin Robyn in the quaint seaside town of Dead Man's Cove, known as the "Sea Monster Capital of the World." But that's just a gimmick for the tourists, no one really believes in sea monsters, right? While cleaning up the beach, the boys make an amazing discovery; trapped in a fishing net is none other than Sigmund the Sea Monster. The boys bring Sigmund back to their clubhouse where they free him from the net. Along with Robyn, the boys and Sigmund become fast friends. A salty sailor named Captain Barnabas (played by David Arquette) has spent his life searching for sea monsters. When Aunt Maxine discovers his net near the clubhouse, she returns it to Barnabas and he begins to snoop around, hopeful he's close to landing his big catch. Sigmund's brothers, Blurp and Slurp, are hot on his trail too. When they come looking for Sigmund, he reluctantly agrees to return with them in order to protect his new friends. But as they make their way back to the beach, Sigmund once again falls prey to one of Barnabas' sea monster traps. Sigmund is trapped and Captain Barnabas is about to reveal him to the entire world! Can the kids find a way to save their new friend and still keep the existence of sea monsters secret?