Dave stumbles across a mermaid at the dockside who invites herself round for tea and takes up residence in the Spuds' bathtub, so Dave and his family must somehow persuade their unwanted guest to go back to her watery home.

Dave finds a handheld computer game at the dump which involves killing zombies - his friend Zombie Katie, however, finds the game rather insulting. Exacting her revenge, Dave finds himself confronted with a group of very angry and very real zombies.