Doctor William Barton was a brilliant and wealthy surgeon. However he was also a mentally unstable man. He was prone to violent paranoia, especially concerning his rebellious wife Marcia Barton, and would eventually murder the man he suspected of having an affair with her. Barton sought to use the Gill Man for his planned experiments in surgically evolving living creature. Along with Marcia, guide Jed Grant and his three colleagues Dr. Morgan, Dr. Borg and Dr. Johnson, he went into the Florida Everglades in search of the creature, where it had last been seen since escaping from Ocean Harbor Oceanarium.
The Gill Man, already wounded from an encounter with a Florida native named Morteno, proved fairly easy to capture when Barton and his team went out after him in a motorboat. The creature attacked and climbed into the boat with them. In trying to use a gas can as a weapon, the Gill Man doused himself with gasoline and was set alight when Grant threw a kerosene torch at him. Barton and his team took the dying Gill Man aboard the research vessel Vagabondia III, where they discovered that beneath the burned-away gills and scales were lungs and a layer of human-like skin. They performed emergency surgery on the creature, saving his life and giving him the ability to breathe out of the water. During the voyage home tensions soon mounted between Barton and Marcia, and with Dr. Morgan who did not like the idea of changing the Gill Man's physiology.
A decidedly unfriendly relationship was also developing between Barton and Jed Grant, whom Barton suspected his wife was having an affair with behind his back. Once they returned to the Barton residence and secured the Gill Man in an enclosure, the fiercely jealous Barton ordered Grant to leave. When Grant gave him lip, Barton flew into a rage and pistol-whipped the poor man to death. Suddenly afraid of going to jail for murder, Barton panicked and tried to blame the Gill Man for the death by putting Grant's corpse into the creature's enclosure. But the Gill Man, having seen the murder, broke loose and came after Barton. After a lengthy chase through the house, the Gill Man finally caught up with Barton and, lifting him up, hurled him off the second-story balcony to his death.