When the kids realize Maxine might have to shut down the Tater Tower, they are desperate to fundraise so they can stay in town with their friend Sigmund. Meanwhile, a recent realization leaves Barnabus reconsidering his feelings on sea monsters.
With Sigmund's help, Robyn and Johnny try to win this year's sand castle contest. Sadly, Sigmund gets sick and the kids need to figure out how to make a sea monster healthy! Scotty's robotic vacuum is mistaken for a pet by Slurp.
Sigmund makes a present that Robyn gives to her mom, Maxine, who is impressed with Robyn's artwork! Robyn plays along but her true talents are soon revealed. Barnabus coerces Johnny to help him plan a surprise gift.
The brothers teach Sigmund about “dibs” -- but he misunderstands and starts stealing from the town! After Sigmund's dibs pile is discovered, the brothers try to get the goods back to their rightful owners, all while pretending that Sigmund doesn't exist.
Divided by their situation, the brothers and Sigmund try to reunite. But Captain Barnabus' quest to prove sea monsters exist and Sigmund's overbearing family threaten their hopes of finding each other.