This issue begins with a lost spacecraft, with the occupant talking about how he just put the other passengers to sleep. We see that it's the chimp, Dr. Milo. Then, we go to five years before Taylor appeared. Milo has discovered that the recent destruction of the moon will soon destroy all life on Earth, but Zaius doesn't seem all that concerned. So Milo continues his lone forays into the Forbidden Zone, searching for a possible solution to apekind's predicament in man's ancient books. He stumbles upon the lair of the human mutants and is taken prisoner for years. Although he's routinely tortured, he connects with one of them. The mutants are split--half want to continue their existence, the other half want death. And the bomb they worship is the twin to the one that obliterated the moon. Most surprising of all, Milo finds out that General Ursus is really a mutant masquerading as an ape!
The mutant woman lets Milo go and he sees that the Zone is connected to Painted Valley, where the Ape mutants live. When he returns to Ape City he tries to warn Zaius but the orangutan refuses to listen. And Ursus threatens him. He goes to Prisca, who he hasn't seen in years and learns about the speaking human, Taylor. This interests him because Taylor said he came from another world. When he confronts Cornelius and Zira they don't want to get into any more trouble--but give him a hand drawn map of the direction where Taylor has been. Milo in an ox driven wagon, follows the directions to that bleak area of the Forbidden Zone and comes to where Taylor's ship crash-landed in the water. With the oxen, he manages to drag it out. He repairs as much as he can but one important piece was destroyed. Then, he sees something flaming in the sky. He follows to where it crashed and discovers a crashed ship. Everything is burnt--except the piece that he needs to power the other ship. He believes that the Lawgiver smiled on him that day. But how does he know how to launch and operate the ship? From the mutant woman who helped him--she telepathically gives him the information. Milo gets his crew with Zira, Cornelius and Zira's nephew, Lucius, but they are attacked by gorillas. Lucius is shot and killed. It story ends with Milo on the ship telling this story--and them crashing into the ocean of a new planet. He realizes it was time, not space, the ship went through. The last image is of the three ape astronauts standing on the beach, looking at all the 1970's humans...
This concludes the series and answers a lot of questions I had, at the same time tying together the first three original POTA movies. Highly recommended.