It's hot in Gotham City but an iceberg hits a yacht in the harbor and a villain identifying himself as Mr. Freeze robs the passengers. Bruce gets word of the crime and interrupts Alfred's planned vacation to go hunting, using an infrared sensor to pick up Freeze's trail. Freeze is breaking into a jewelry store when the Batman interrupts him. Freeze claims they're having a "reunion" but Batman doesn't know who he is. Freeze lowers the temperature of the entire room to slow down Batman. Batman manages to part his helmet long enough to see Mr. Freeze is "Victor Fries," and then Freeze ices him in a block of ice.
Freeze reveals that Batman had once pursued him when he was a mere bank robber. During the high-speed chase Fries' car was wrecked when a homeless man crossed his path and he fled into a cryonics laboratory. While trying to use the frozen gases to escape, Fries was caught in a malfunctioning cryonics chamber and simultaneously electrocuted and froze. When he later escaped, Fries discovered he could manipulate cold and obtained a special suit to contain his temperatures.
The police show up and Fries escapes, leaving Batman behind. Bruce manages to escape before the police can unmask him and barely makes it back to the Batcave where Alfred tends to him. Freeze continues on his rampage and spots the homeless man who caused him to go off the road. Bruce gets a fever and is uncertain whether he should continue as the Batman. He starts to hallucinate about his parents and sees Freeze as the one killing them. His resolve strengthened, he goes out with special thermal gear to Gotham Central Park where Freeze is.
In his new suit, the two are evenly matched. Batman remote-activates the Batmobile and, using a pair of flame guns, distracts Freeze long enough to hit him with the car's heated exhaust, knocking him out. The Batman escapes as the police move in and capture Freeze and Bruce returns for a cup of hot tea.