This theme's about mermaids and mermen battling against evil invaders that are trying to destroy their home and take control of the ocean. The invaders, which are wearing heavy armor and diving masks, have one "evil" red staff. The merpeople have the "good" blue staff. Whoever has both of these staffs together has complete control over the seas, so the invaders want to take it from the merpeople of the city Mermonia. Luckily, the king of Mermonia has a young son, the prince of Mermonia, who is battle hardened and will do any thing to help his people and protect the princess. The main picture is of a set that would invaders attacking a Mermonian outpost. Minifigures included are 2 Mermonian soldiers, the prince, and 2 invaders. Also included is an underwater outpost, an invader vehicle, and 2 invader mini tanks.