Jessie and the children take a vacation on the Ross family's yacht for their one-month vacation. While on vacation, the Ross family finds a girl stranded in the middle of the ocean and invites her aboard their yacht. Luke develops a crush on the girl, and Zuri believes she's a mermaid. Meanwhile, Bertram stays home and babysits Mrs. Kipling, who has separation anxiety from Ravi.
After Bertram joins Jessie and the Ross children's vacation, they go exploring on an Italian island. Their tour guide tells a story about Jessie's necklace and how its curse brings anyone who wears it bad luck. Meanwhile, Luke and Ravi attempt to try firewalking in order to impress girls.
Jessie abruptly ends the Ross family vacation because the kids are constantly fighting. She decides to dock the ship so they can return home on a plane. They wind up in a pickle when they find the yacht the next morning floating in the middle of the sea with no captain or crew in sight. They must work together to save the ship and each other when a storm approaches.