M.O.D.O.K., who was at the time the leader of the subversive organization called A.I.M., discovered Betty's condition and decided to take advantage of it. In order to create a creature powerful enough to defeat the Hulk, he infused an incredible amount of gamma radiation into her, making her the monstrous and insane Harpy. The dreadful creature broke out of a special shell, immediately wanting to know where the Hulk was so that she could kill him.
M.O.D.O.K told Harpy where to find the Hulk, and she flew off to find him.
The Harpy soon found the Hulk, ambushing him and engaging in combat. The two fought each other without hesitation, but before the Hulk landed the killing blow, the Harpy told him she was Betty. The Hulk, shocked and confused by her statement, is blasted unconscious by the Harpy.
General Ross saw the Harpy and the Hulk fighting on TV and recognized his daughter. He made his way as quickly as possible to the battle site, running to talk to her right before she blasts and tries to kill the Hulk. Ross tried to convince her that she was a gentle human being, but still under the influence of M.O.D.O.K.'s brainwashing. Thinking his words to be a poor trick, the Harpy flew away with the Hulk in her clutches.
When the military sent out fighter jets to try and stop her, she shot one out of the sky before she and the Hulk were swept up in a strange tornado that pulled them into a giant cloud mass. They soon found themselves in a strange city hidden in the clouds. As the Hulk revived, they were confronted by a two-headed creature calling itself the "Bi-Beast". When it grabbed the Harpy out of interest, she lashed out with gamma ray blasts, and the Hulk, wanting to protect Betty, attacked the creature as well. The Harpy was easily knocked out with a single blow, but the Hulk proved to be more of a challenge. Despite the fight the Hulk put up, however, the thin air in the upper-atmosphere brought him to defeat. He collapsed from a lack of oxygen and reverted back to Bruce Banner.
When Banner revived he explained to the Bi-Beast that he was a scientist, leading the creature to believe that destiny had brought him to the floating island. It told Banner that the island was created by the "Bird People" and the Bi-Beast was created to be a living monument of their achievements once they passed on. It explained that the machines holding the city in the air were starting to break down and that they had no knowledge on how to repair them. It asked Bruce to use his skills to save the city, with the predicament now known. Additionally, it explained that it captured the Harpy because they yearned for the company of someone that resembled their creators. The Harpy fit that description.
Bruce, not knowing how Betty's transformation occurred, figured he could use the advanced equipment to try and help her. He went looking for the Bi-Beast, finding it trying to communicate with the reluctant, caged Harpy. Bruce said he would help repair the equipment if the Bi-Beast let him take the Harpy with him, to which the Bi-Beast agreed. Bruce gathered equipment together he suspected would cure Betty. Unbeknownst to him, M.O.D.O.K came to the island looking for both him and the Harpy. He tricked the Bi-Beast into thinking Bruce was going to betray him. The Bi-Beast, fooled, attacked Bruce just as he hit the switch to start the equipment. A fight ensued, angering Bruce and turning him into the Hulk. The successful M.O.D.O.K double crossed the Bi-Beast and attacked it. As the Bi-Beast hit the self-destruct button, the Hulk became Bruce once more and went to search for Betty. He found her in the device still as the Harpy. He was devastated due to the apparent failure of the machine. Nevertheless, he grabbed her, became the Hulk, and made a run for it as the island fell apart. As the Hulk ran in attempt to bring them both to safety, parts of a building from the island fell on top of the Harpy. When the dust cleared, the Harpy had reverted back to Betty Ross.
Betty's transformation was reversed permanently after the encounter with the Bi-Beast. She regained both her normal form and her sanity, showing that Bruce's machine was successful.