(First Aired: October 30, 1966)
Screenplay by: Kitao Senzoku
Directed by: Toshihiro Iijima
The rocket Ohtori is being prepared for the first expedition to Venus by its inventor and pilot Professor Mohri. Science Patrol has been asked to accompany the rocket, so Hayata is placed in the Jet V-TOL. Ohtori launches with the V-TOL following immediately. Ohtori proves to be ridiculously fast and soon leaves the V-TOL behind in Earths atmosphere. With the operation a success, Science Patrol decides to take the time to relax with some coffee.
In the midst of the enjoyable coffee break, a glum Hoshino comes in. Hoshino is unhappy that Dr. Iwamotos Phoenix had lost to Ohtori. Muramatsu assures Hoshino that Iwamoto did not actually lose to Mohri, but simply wanted to ensure Phoenix was 100% flawless. This is just what Hoshino needs to raise his spirits. Meanwhile, Ohtori has entered Venus orbit, so Science Patrol watches Professor Mohris activity in the ship via live feed shared with ground control. Suddenly the feed is distorted by what Fuji reports to be a strange message. Ide suggests that the message is alien in origin, so the team hooks up their Pan-Space Translator to the main computer. With that, the feeds jumble is replaced with a familiar face Alien Baltan! This new Baltan explains that after Ultraman destroyed their ship in their previous appearance, survivors had fled to a new world, Planet R, as a temporary settlement until Earth could be conquered.
As for Professor Mohri, an orb-like spacecraft slams itself into Ohtori. Mohri sends out an S.O.S., but when Science Patrol contacts him, he assures them that it was probably just an Earth satellite. Science Patrol, however, believes Baltan is behind the collision. Needing a way to check on Ohtori, Science Patrol contacts Dr. Iwamoto to use his Phoenix. Iwamoto refuses, as if the attcker really was Baltan, then Phoenix would be useless for space combat. Instead, he suggests equipping the V-TOL with a special rocket engine he made for it. Back in space, Ohtori has been mysteriously drained of all its fuel, leaving Mohri helplessly floating about. Baltan then teleports himself onto the ship and takes over the body of the protesting Mohri.
Back on Earth, the Jet V-TOL is equipped with Iwamotos engine a Hydrogenate Rocket, which can be used in both Earth's atmosphere and space. The possessed Professor Mohri shows no interest in being rescued though, and he calls in a normal-sized Baltan, which is small enough to stand on a human palm. Baltan/Mohri instructs the tiny Baltan to begin an invasion of Earth. The seizing of the Ohtori was merely a distraction for Science Patrol. With that, the Baltan mothership the orb-like spacecraft from earlier heads to Earth.
On Earth, Muramatsu, Hayata, and Arashi launch off towards Ohtori. Meanwhile, Ide finds the Baltan ship and goes after it in a second Jet V-TOL. Hundreds of now man-sized Baltans begin to exit the ship and turn the tables on Ide. Fuji, witnessing the scene from HQs screens, reports to Muramatsu that Baltan has tricked them. Despite the alarming situation, the team continue towards Ohtori, planning to return once Mohri is saved.
While Ide blasts Baltans out of the sky, the rest of the men bring Mohri home, unaware of his current state. Baltan/Mohri sabotages the Jet V-TOLs controls, and the ship crashlands on Venus. The Science Patrol eventually regains consciousness and spot Mohri outside the ship. Arashi and Muramatsu go after him, but Baltan/Mohri pins them down with telekinesis. Baltan/Mohri then flees off to a safe spot, where Baltan exits Mohris body and turns giant-sized. Taking no more of it, Hayata becomes Ultraman!
Ultraman begins the battle by firing a Specium Ray. However, Baltan has come prepared as he reflects the ray with his new Spellgen Reflector, specifically designed to deflect Specium energies. Ultraman simply switches tactics and cleanly slices Baltan in two with a bladed energy ring called the Ultra Slash. Ultraman then teleports himself to Tokyo (at the cost of some of his Color Timer energy) to challenge the Earth invasion. The Baltan swarms merge themselves into a single massive Baltan to fight one-on-one. The second giant Baltan soon meets the same fate as the first one, and with that, Ultraman flies off.
On Venus, Muramatsu and Arashi find the weakened Dr. Mohri and take him to safety. Unfortunately, it seems they have no way to get back to Earth now that the Jet V-TOL has been damaged. Then, Iwamotos Phoenix lands down on Venus, and out of it comes Ide, Fuji, Hayata, Hoshino, and Iwamoto. Soon, Phoenix launches off with everyone on board for the voyage home.