On what seems to be a normal day for the Earth, a massive invasion fleet of alien ships mass near the moon. The SSSP's Paris base radios in at the SSSP base in Japan that the coming fleet may very well be the largest invasion fleet ever deployed against the Earth.
Taking matters into their own hands, the SSSP, sans Fuji and the visiting Dr. Iwamoto, take to the skies in their VTOLs and easily wipe out many of them. Unfortunately, back at the base, Iwamoto attacks Fuji and proceeds to destroy the base's supercomputer. Soon, Hayata, Captain Muramatsu, Ide, and Arashi return to find the base in chaos. Ide assists Fuji while his comrades chase down Iwamoto. Arashi catches up with the latter, and punches him, revealing the face of an Alien Zetton, who'd incapacitated the real Iwamoto beforehand. Hayata quickly shoots the alien, who simply says 'Zetton' before evaporating. Suddenly, a final alien ship, much bigger than the ones that had been destroyed earlier appears and unleashes a monster called Zetton.
While Arashi runs back to the base to rescue Fuji and the real Iwamoto, Hayata transforms into Ultraman and soon, the silver giant and Zetton clash. In the ensuing battle, Zetton damages Ultraman's Color Timer, leaving him unable to fight. But Ide and Arashi then shoot Zetton with Dr. Iwamoto's creation, a special anti-gravity missile that kills the monster.
Soon after, Zoffy, an Ultra Warrior of higher rank than Ultraman, arrives in a Travel Sphere to revive his comrade. The two engage in conversation. (In the Japanese original, Zoffy debates with Ultraman about Hayata. In the English version, Zoffy, who is not mentioned by name in this version, inquires about why his subordinate has lost to Zetton, and is told about Zetton's use of the unexpected weapon that damages Ultraman's warning light.) Ultraman requests that Zoffy split his and Hayata's life forces that Hayata may live a normal life, and also that he may regain his own powers and return to Earth. Zoffy complies with both requests, and Hayata ends up where Ultraman had fallen. The SSSP wave Ultraman goodbye, and a clearly amnesiac Hayata is left with the Beta Capsule. (In the English version, Hayata keeps his memory and joins his friends in seeing Ultraman and Zoffy off.)
As the narrator promises that Ultraman will return to the Earth someday, the last shot of the series is Zoffy and Ultraman flying home together back to Nebula M78.
- Toshio Muramatsu (ムラマツ・トシオ Muramatsu Toshio): Akiji Kobayashi (小林 昭二 Kobayashi Akiji)
- Shin Hayata (ハヤタ シン Hayata Shin): Susumu Kurobe (黒部 進 Kurobe Susumu)
- Akiko Fuji (フジ アキコ Fuji Akiko): Hiroko Sakurai (櫻井 浩子 Sakurai Hiroko)
- Daisuke Arashi (アラシ・ダイスケ Arashi Daisuke): Sandayū Dokumamushi (毒蝮 三太夫 Dokumamushi Sandayū)
- Mitsuhiro Ide (イデ・ミツヒロ Ide Mitsuhiro): Masanari Nihei (二平 政成 Nihei Masanari)
- Dr. Iwamoto (博士岩本 Iwamoto Hakase): Akihiko Hirata (平田昭彦 Hirata Akihiko)
- Ultraman (ウルトラマン Urutoraman): Masao Nakasone (中曽根雅夫 Nakasone Masao) (grunts), Hisashi Kondo (近藤久 Kondo Hisashi) (voice)
- Narrator (ナレーター Nareta), Zoffy (voice) (ゾフィー Zofī): Hikaru Urano (浦野光 Urano Hikaru)
"Ultraman, open your eyes. I am Space Patrolman Zoffy, from Nebula M78. Now, come back to the Land of Light with me, Ultraman."
"Zoffy, my body does not only belong to me. If I go home an Earthling will die."
"Ultraman... you've done enough for Earth. The Earthlings will forgive you."
"Hayata is truly a great person. I will stay on Earth so he does not have to die."
"It's best to let humans take peace into their own hands. Ultraman, you can not stay on Earth forever."
"Zoffy, I would like to leave Earth by giving my life, to Hayata then."
"You don't care if you die?"
"No, I don't. I have already lived for 20,000 years. Earthling's lives are very short. And Hayata is still very young. I do not want him to be a victim."
"Ultraman, do you love Earthlings that much? Alright, I have brought two lives with me. I'll give one to Hayata."
"Thank you, Zoffy."
- Ultraman Volume 10 features episodes 37-39.
- Ultraman The Complete Series features all Episodes.
- In the original Japanese airing of this episode, Ultraman asks Zoffy to identify himself "Who are you?" But for unknown reasons, this line of dialogue was cut, making Zoffy introduce himself without being asked first.
- However, in the first Mill Creek release, this is retained.
- While Ultraman was dead, flashbacks of when Ultraman fought Gabora from episode 9 and Jirass from episode 10.
- The English version explained that Ultraman's defeat was due to Zetton having employed a weapon that Ultraman had not expected; it had damaged his Color Timer, and he had lost his ability to gauge his remaining strength.
- In the American release, Ultraman's conversation with Zoffy is changed from discussing Ultraman's willingness to sacrifice himself so that Hayata can live to Zoffy asking Ultraman why Ultraman had lost to Zetton, who he claims was less powerful. (This was despite Zetton easily withstanding all of Ultraman's attacks.)
- This episode was later featured in New Ultraman Retsuden episode 142 "Zetton Invasion! Farewell, Ultraman."
- The Ultraman Orb episode, "The Holy Sword, Restored," is a tribute to this episode.