"Return to Tomorrow" is the twentieth episode of the second season of the American science fiction television series Star Trek.
In the episode, telepathic aliens take control of Captain Kirk, Dr. Ann Mulhall (Diana Muldaur), and First Officer Spock's bodies in order to construct android hosts.
Upon arrival, a telepathic being named Sargon (voiced by James Doohan) addresses Kirk and Spock as his "children", and invites them to beam down to the planet.
Sargon explains that he and his companions will need human bodies temporarily, in order to construct android hosts for themselves, and then returns to his orb.
Back onboard the Enterprise, the four meet with Chief Engineer Scott to consider Sargon's request, and Kirk convinces the others with a rousing speech about risk.
When Sargon and Thalassa become exhausted by the strain of the transference, Henoch instructs Nurse Chapel in preparing a serum that will strengthen the host bodies.
They make a final request, which is granted: to be allowed to use Kirk and Mulhall's bodies one last time to share a kiss.
Michelle Erica Green of Trek Today writes that the story is "an entertaining and engaging episode about power, loyalty and the struggle between physical and mental pleasures... and because there's an alien in his body, Spock spends a lot of time smiling".
Of the characterizations, she adds, "Nimoy appears to be having a wonderful time playing a relaxed, calculating villain, and Shatner portrays Sargon in an amplified booming benevolent voice that makes a nifty contrast to his would-be-Kennedyesque speechifying, expounding on the values that sent humans to the stars".
She argued, though, that a "big and frustrating plot hole" is Sargon's dismissal of the idea that Starfleet might build them android bodies.
These android bodies seem perfectly suited to Sargon's people, and it's annoying that the lack of series continuity kept it from being mentioned".
[3] Eugene Myers ranked this as a superior example of "several bodyswap/alien possession episodes of the series" in terms of acting: Shatner has a "nuanced performance, walking jerkily as though unaccustomed to legs after eons without a body", while "Nimoy, of course, clearly enjoyed the opportunity to stretch his acting—and facial—muscles, playing out of character ... to smirk, smile, and scheme his way through his scenes".