After a recap of his origin, we see the Hulk break out of his cavern prison and battle a team of soldiers conducting war games. Later, when UFO sightings in Rome are reported, Rick Jones persuades Bruce Banner to go over and investigate in order to stay out of sight of General Ross. Their mission fails when the stress of a difficult landing at Rome's airport causes Banner to transform into the Hulk. He escapes by smashing through the plane's hull, leaving Rick alone in a foreign land.
Meanwhile, invaders from Krylor have established a base at the bottom of the Tyrrhenian Sea and are planning to infiltrate Earth by taking on human forms. But first, they must capture Bereet, a renegade techno-artist from their world who has stowed away on a Krylorian warship and is now free on Earth.
That night, Bruce Banner awakens on the Spanish Steps and is mobbed by the city's predators, triggering his change into the Hulk. One of the thieves is revealed to be a disguised Krylorian who attempts to capture the Hulk. After he is soundly defeated, he tells Hulk that the Krylorians are police sent to capture the fugitive criminal Bereet.
At this point, the Gargoyle appears (the explosion in Incredible Hulk #1 (1962) didn't kill him but caused him to revert to his mutated form) and persuades Hulk to join forces with the Krylorians.
Rick Jones is found by Bereet (who turns out to be a beautiful woman) and learns the truth about the Krylorian plans. Hoping to find the acceptance on Krylor he has been denied on Earth, the Gargoyle allies himself with the aliens and sends the Hulk to capture Bereet.
Hulk locates the renegade techno-artist and prepares to capture her when the Krylorians open fire on them all. Realizing he was tricked, Hulk battles the alien saucers and, with the help of Bereet and her Banshee Mask (which transforms her into a warship) plus the aid of the Gargoyle who discovers hes been duped as well, and sacrifices himself to destroy the enemy flagship!
The surviving Krylorians flee to their undersea base, and the Hulk vows to drive the invaders out with the help of Bereet and her bag of tricks.