[9.1/10] I sang the praises of D.C. Fontana in my writeups for *The Original Series*, so I won’t spend much time rehashing them here, but I’ll say this much -- she is such a boon to Star Treks of all shapes and sizes. I don’t think there’s a writer, particularly from the *TOS*-era of the show, who better understood that for all the science fiction wizardry at play, you have to nail the characters and their experience of all that futuristic brick-a-brack to turn out the best *Star Trek* episodes. That’s what’s great about “Yesteryear.” It has a fantastic sci-fi premise that involves our heroes returning to The Guardian from “City on the Edge of Forever” and having more back-in-time adventures. I find it amusing that despite the kind of ominous threat and danger The Guardian posed in its first appearance, now Starfleet is using it to casually explore the past and employing it as a historical DVR. Naturally, this goes wrong, and when Kirk and Spock return from visiting the dawn of the society on Orion, nobody remembers who Spock is. The explanation is a little headache-inducing, but also elegant. In this timeline, Spock died when he was seven-years-old. Kirk and Spock, who are sure that they didn’t interfere with the past in any way in their trip to ancient Orion (“I swear I didn’t touch that slave girl!”), try to piece together what happened. In a neat bit of clockwork time travel plots, Spock recalls that an older cousin, Selek, helped the young Spock when he was going through the Vulcan trials in the desert at the time of his death in this timeline. Though the memory is vague, the adult Spock realizes that *he* was Selek, and he has to go back through The Guardian now to complete the stable time loop. Some of the chronological tricks used to get there feel a little contrived. Apparently the fact that Kirk and Spock were using The Guardian to travel back in time to Orion at the same time some other Starfleet dignitaries (including some wild pterodactyl man!) were reviewing the history of Vulcan at that time meant that Spock “couldn’t be a two places at once” and messed up the time loop. It’s kind of hard to wrap your head around, but makes enough surface-level sense to pass the smell test. But what’s great about “Yesteryear,” and Fontana’s scripts generally is that the episode doesn’t just coast on the “hey, isn’t it cool to go back in time!” novelty of The Guardian. It uses Spock returning to his childhood home and visiting with the moppet version of himself as a means to elucidate the struggle Spock had growing up between honoring his Vulcan side and his Human side. It spotlights Spock’s difficult relationship with his father. It lets Leonard Nimoy shine as a voice actor as the elder Spock speaks knowingly with his younger self. The best feature of the episode is how it presents the audience with the elder Spock we know and love -- stoic, measured, and disciplined -- and a young Spock we’ve never seen before -- headstrong, uncertain, and emotional -- and naturally makes the viewer wonder how he got from A-to-B. “Yesteryear” doesn’t give every detail (it doesn’t have the time afterall), but it presents a seminal moment in young Spock’s life that set him on the course to being the noble Vulcan man he is today. That moment hinges on I-Chaya, Spock’s childhood pet sehlat. (Think of a cross between a dog and a saber toothed tiger.) It’s clear that the I-Chaya is very important to young Spock. His mother mentioned it in “Journey to Babel,” and this episode takes care to mention that it first belonged to Sarek so it’s a family pet and part of his legacy. At the same time, it’s clear from young Spock being derided by his peers as an “Earther,” warned by his father about the difficulties of their way of life, and speaking with a mother who wants to honor the Vulcan ways she’s adopted, that I-Chaya is Spock’s dearest friend and closest confidante. That’s why it’s meaningful when I-Chaya saves young Spock from a wild le-matya (think of a cross between a dragon and a wolf), young Spock has to try to repay his friend. “Selek” helps young Spock figure that he needs to run to town to fetch a healer if he has any hope, disclaiming his prior practical jokes in the process. When the healer explains that I-Chaya is fatally wounded, young Spock has to choose between extending his furry friend’s life, which would be painful for it, or “releasing” him. It’s a choice between emotion -- wanting to preserve someone young Spock loves, and between maturity -- understanding that all things end and that the right thing to do is grant I-Chaya that one last kindness. There is something poetic about elder Spock, in his guise as a distant cousin, teaching his younger self about Vulcan philosophy. It’s one of the most beautiful accounts of the Vulcan perspective *Star Trek* has ever presented. Spock speaks of Vulcans still experiencing emotions, but not letting themselves be controlled by them, of feeling grief, but only when a life is wasted, of accepting that everything ends but appreciating the time shared before that inevitability. The young Spock is clearly in conflict, struggling with whether he can be what his father wants him to be, whether he can find the center of himself. The act of the elder Spock giving him gentle guidance serve as a tremendous character-building moment for Spocks old and new. There is something wistful about the elder Spock here, where recognizes the difficulties of those times but clearly appreciates his chance to revisit them from a different vantage point. His words to his father about trying to understand his son are about as sentimental as the Vulcan gets, and his half-joking admonition to Bones that, had things been different, the doctor might have had to calibrate his devices for an Andorian, show that there’s still a part of that playful little boy within the older Spock. (And as an aside, it’s a nice beat where the Andorian first officer gives Spock his blessing and goodbye.) Time travel stories are often fun because they often take the shape of what-ifs. It’s exciting to imagine what might have been if some detail were changed, or gawk at the precursors and causes to the present day effects. But Fontana uses that to explore the distance between a child and an adult, those life-changing moments where we choose who we are, and the reflections on what we became and what we lost in the process. There is great poetry in that, a sort of it hardly possible outside of the science fiction context, and “Yesteryear” embraces it to the fullest.