Part 1: "The Merciless Puppet Master"
The Fantastic Four are returning home after having defeated the Red Ghost on the Moon ( Fantastic Four #13). Upon landing at Idlewild Airport, they are greeted by a massive crowd. Each member of the Fantastic Four has their own problems as people all want something from them. The Human Torch whisks the team off to the Baxter Building by creating a warm air funnel.
Back home, Mr. Fantastic finishes his report on the moon trip for NASA, then goes looking for the Sue. He finds her, operating his "Roving-Eye" camera, which is focused on the bottom of the sea. He guesses that she is searching for Namor, and then realizes that for all of his powers and intellect, he still can't conquer Sue's heart.
Meanwhile, at a sanitarium, the Puppet Master receives a discharge, having been deemed sane. He reveals that he survived the fall after his fight with the Fantastic Four, and has been hiding for months to let the world forget him. The Puppet Master then decides that he'll use a scapegoat to fight the Fantastic Four, and after going through some of their past enemies, decides to use Namor to fight them for him!
The Puppet Master makes a puppet of Namor and makes Namor in turn contact Sue Storm, and tell her to meet him at the New York docks. Upon Sue meeting Namor at the docks, without telling the other members of the Fantastic Four what she's doing, Namor uses a Hypno-Fish to hypnotise her. Sue is then placed in an air bubble and taken under the sea, whilst the Puppet Master thinks that his plan is working out.
The Fantastic Four are then contacted by Namor and told to fight him, and shortly afterwards they leave, with the exception of the Thing, who goes to visit Alicia Masters beforehand. Alicia is worried for the Thing, and for what she'd do without him, and so the Thing agrees that she can come with them. The Fantastic Four all then go into the ocean with an experimental bathysphere, and after Namor sends a few sea creatures at them, he manages to capture them with a giant clam. Namor then reveals that Sue is trapped in a glass sphere being attacked by a giant octopus, and that they have to defeat him to rescue her. The Fantastic Four then start fighting Namor, and after a short while, Mr. Fantastic attacks Namor on his own whilst the Thing rescues Sue. The Puppet Master sees this, and decides that the Fantastic Four are too powerful, and so controls Namor to kill them instead of just defeating them.
Whilst Namor is threatening the Fantastic Four, Alicia senses a mental prescence, such as that of the Puppet Master. Namor then almost kills the Fantastic Four using a gas from a sea plant, but Mr. Fantastic saves them with his Flex-O-Gen packets. The Fantastic Four are then about to attack Namor again, but Sue stops them, saying that he was being controlled and is innocent. The giant octopus which the Thing got rid of from attacking Sue has by now reached a submarine where the Puppet Master was watching the fight, and attacks him. As this happens, the Puppet Master's control over Namor is gone, and so Namor orders the Fantastic Four out of his realm, which they agree to.