• “Side-By-Side with Sub-Mariner!” – Reed Richards is examining a massive sea creature which had washed ashore. Suspecting that it may have come from Namor’s domain, he dispatched the Human Torch to check along the shoreline for any signs of danger. He spots an Atlantean woman rising out of the water and takes her back to the Baxter Building. There Sue recognizes her as Lady Dorma, Namor’s beloved. She explains that she has come to seek the Fantastic Four’s aid as Atlantis has been attacked by the barbarian hordes of Attuma, a fierce warrior who believes he is destined to rule Atlantis. She goes on to explain that she blames herself for Attuma’s advantage in battle, as when Dorma expressed her fears of his harm in battle he dismissed her. Heartbroken, Dorma then showed Attuma and his minions a way to get past Namor’s defenses.
Regretting her decision, Dorma rushed to the surface to seek out allies to help stop the invasion as the surface world would be at risk next. The Fantastic Four agree to help out and this time Reed has developed new inventions that will assist them in undersea missions. With his Oxy-Spray, Reed makes it so his teammates can breath underwater for hours at a time, the spray is so potent that even Johnny can use his flame powers underwater.
As soon as they approach Atlantis in their submarine, the Fantastic Four are attacked by Attuma’s hordes and are forced to abandon ship. They battle their way through the soldiers and weapons. Meanwhile, in the kingdom, Namor and his forces fight back against the invaders. When the Fantastic Four arrive, Reed cautions his team to remain hidden as Namor may also view them as his enemies. Sue uses her invisibility powers to destroy subsonic weapon. As Namor and Attuma battle it out, the Fantastic Four secretly keep Attuma’s minions from interrupting the battle. As the battle rages on the Oxy-Spray begins to wear off. After Namor destroys Attuma’s sword, Attuma surprises him by revealing hidden disintigrator rays. But the Sub-Mariner is given an upperhand in the battle when Sue secretly turns him invisible. Namor then subdues Attuma as the Oxy-Spray begins to fully wear off forcing the Fantastic Four to flee back to the surface before Namor could learn how they helped him that day.
In the aftermath of the battle, Attuma is defeated and banished from Atlantis. Later Namor reveals that he knows that Dorma betrayed him, but that he forgives her out of love. Meanwhile, the Fantastic Four are stuck using Reed as a buoy at sea as they left their submarine below the water. On the way home, Sue calls Reed darling, making him wonder if she has finally forgotten about her feelings for the Sub-Mariner.