Tsutomu, son of scientist Professor Hayashi, lives in a distant future. He forms a close bond with stray dog Queen and her three puppies—Ace, Jack, and Joker. When alien invaders from Planet Devil target his father, the dogs sacrifice themselves to intercept an alien bomb disguised as a cactus, physically perishing. Professor Hayashi preserves their brains, integrating them into specialized cybernetic bodies gifted to Tsutomu on his birthday. The enhanced canines possess distinct combat abilities: Queen acts as a power source equipped with a nasal drill, Ace features multi-purpose vision and a plasma gun, Jack emits destructive gas, and Joker functions as a shapeshifter. Tsutomu receives a helmet enabling communication with the dogs and later inherits his father's automatic ray gun.

After an alien attack mortally wounds Professor Hayashi, Tsutomu assumes leadership of the cyborg dogs. He pilots their combined form, the spaceship "Liner," to combat the alien threat. The invaders plan to detonate the Moon to destroy Earth. Tsutomu directs the Liner to infiltrate their hollow planetoid ship near the Moon, damaging the vessel. He prevents the Moon's destruction by disabling the bomb timer with less than a second remaining. To ensure Earth's safety, Tsutomu rams the Liner into the fleeing craft of alien leader Golgoth. His actions neutralize the alien menace and safeguard the planet.