The older Sulu explains that the Gorn had been banished to their homeworld by the Metron (after the Gorn had lost a staged fight with Captain Gary Mitchell). However, the Gorn had later found a way to transport directly to other planets, and had conquered the Romulan Empire and much of Federation space, and Sulu had been attempting to destroy the hub of the Gorn’s transportation system when he suddenly found himself on Tlaoli. The younger Sulu, together with his shuttle, finds himself flying over a different planet (later he learns it is called Basaraba), and under attack. He escapes from his attackers, but crash-lands the shuttle. When he sends out a signal on a Federation hailing tone, he immediately gets a surprised call from an older Chekov, and the two of them work together to destroy the Gorn’s hub. Meanwhile, Spock has come down to the planet to try to resolve things, and they discovered what appeared to be a control panel for the transportation device, known as the Janus Gate, that had switched versions of Kirk and Sulu. After some experimentation, they discover that the device was used to recover wounded warriors from battle, and replace them with fitter versions, and the device does transport through time and space. They find that the young Kirk had been about to be killed by Orions, just before he ended up on Tlaoli. Spock attempts to transport the older Sulu back to his time, but the device does not see him as fit enough to go into battle. An attempt is made to have Chekov go as a traveling companion, but that also fails. Then Uhura tries to act as the main transport person, and she gets partly transferred, so she can see what is going on at the other planet, but can still talk with Spock and the others. Unfortunately, she (or as of much of her as is transported) gets captured by the Gorn and held prisoner along with a captured Metron (who is kept drugged by the Gorn and is the source of the transportation method they use, because the Metrons exist on a number of planes). Spock is able to transfer clean air from the caves to the place where Uhura and the Metron are held, releasing the Metron from her drugged state, and she transfers Uhura, Sulu and the older Chekov back to the caves on Tlaoli. But then a large quantity of mechanical creatures, who call themselves the Shechenag, appear in the caves (apparently controlled by biological creatures inside the mechanical ones). They give the Enterprise group ten hours to leave, and forbid further use of the mechanism that has disrupted the timeline.