The team takes a vacation on the cruise ship “Holiday” combining business with pleasure. There have been sightings of large sea creatures within a span of the Atlantic Ocean. Alicia Masters tags along. Upon investigating creatures they see from the deck of the ship they are captured by the creatures and delivered to Namor who had orchestrated all this.
Namor wants the team to deliver a message to the world above – all oceans and the air above them are under his domain and humans may not pass through them. Namor flirts with Sue but Sue sides with the team. He then sends them back to the surface. Alicia is left on the boat to finish the voyage on her own.
Reed Richards calls an emergency meeting at the United Nations to explain the threat. Dr. G.W. Falton (Namor in disguise) is asked to explain the history of the undersea race (homo mermanus). He recounts how Princess Fen met Captain McKenzie, married him and bore his son – Namor. Richards calls on the nations to battle Namor. Namor then pulls out of his costume, flees to the coastal waters and launches an attack on New York City.
The city quickly falls to him but the Fantastic Four battle to win it back. The Thing takes a prisoner which gives Reed an idea. The mechanism is used and the water in Namor’s army’s helmets begins to evaporate sending them back to the sea. In a rage Namor flies to the Baxter Building, kidnaps Sue and takes her back to his kingdom.
As Namor battles the three male team members, Krang deduces that Namor abducted Sue because he cares for her. This sends Lady Dorma into a jealous rage. Dorma breaks a window allowing sea water to rush in. During he confusion Sue escapes into the ocean without any means of breathing. Namor and the Thing see her and rescue her, stopping the battle. Namor boots all Atlanteans out of his Imperial Command Car to use it to get Sue to a hospital. Krang and Dorma confront him on his concern over the health of an enemy combatant (Sue). Namor demands silence claiming it is his imperial privilege.
Namor rushes her to Manhattan General Hospital and leaves her in the doctor’s care. The other three catch up within a few hours and Sue is recovering. When Namor returns to New Atlantis he finds it deserted – his people abandoned him because of his loyalty to Sue.