After studying the remains of Mecha-King Ghidorah the UN begins work on Mechagodzilla. Meanwhile there is a expedition to Adona Island, the scientists there find a giant egg. Shortly afterwards they are attacked by Rodan, who is then attacked by Godzilla. The scientists manage to escape while the two are fighting. Godzilla defeats Rodan, and follows the helicopter in which the scientists escaped in.

The scientists make it back to Japan and begin work in a laboratory, and set up a incubation chamber for the egg. Eventually the egg hatches, and it is discovered that the egg contained a little Godzillasaurus instead of a pteranodon like was thought. It is feared that Godzilla might try and rescue the baby, and sure enough not long after a report comes in that Godzilla is attacking a oil refinery and making his way toward the laboratory. The U.N. prepares Mechagodzilla, and sends him off to do battle with Godzilla. The two meet in the countryside, and Mechagodzilla appears to be beating Godzilla, until a mechanical failure accrues and Godzilla takes advantage of the situation, and defeats Mechagodzilla.

Godzilla continues to the lab, but suddenly turns away when he gets there. It is discovered that the baby can communicate telepathically and must have been sending off distress waves which caused Godzilla to leave. The UN sets up a new plan to kill Godzilla, and they plan to use Baby Godzilla as bait to lead Godzilla were they want to. Baby is sealed away in a canister, while being readied he sends a distress call. Rodan awakes on Adona Island and ventures to Japan to save Baby. Rodan finds baby being carried away by a helicopter over Japan, he quickly destroys the helicopter and carries baby away.

Mechagodzilla is sent out to retrieve the canister, Rodan tries his best to defend Baby from Mechagodzilla, but in the end Rodan is killed. Shortly after Rodan dies Godzilla emerges from the water, and the two fight. Mechagodzilla ends up destroying Godzilla's spinal brain, and shortly afterwards Godzilla is killed and then explodes, the energy from the explosion speeds up Baby's growing process and turns him to a adult sized Godzilla. Baby then destroys Mechagodzilla and goes into the sea.

A screenplay that was pretty close to Godzilla vs. Mechagodzilla 2 (1993) except for the very strange ending with Godzilla blowing up and in the process causing baby to grow huge, a idea that would later make it into the final script of Godzilla vs. Destroyah (1995). I am very glad the this screenplay was further adapted into the Godzilla vs. Mechagodzilla 2 (1993) that we see today. The idea of killing off Godzilla, and then replacing him with his baby all in the length of one movie seems far too sudden, and I am sure that fans would not have been to happy with the idea.