When dealing with almost any sci-fi show, you’re bound to run into an episode or plot arc that deals with time travel. I figured it would be just a matter of time before Star Trek dipped its toes into the sub-genre, but wasn’t sure how long I would have to wait. Given the recent stretch of expansive episodes we’ve seen, Tomorrow is Yesterday fits right in, and it’s a worthy addition to the season. In fact, both episodes in this installment see Star Trek fit familiar genre tropes into its ecosystem, both yielding fantastic results.

One of the enduring themes throughout Star Trek, and a good deal of sci-fi, is in how we, as humans, are an inferior species, both technologically and mentally. It’s not only a way to build out the universe within the show, but a smart but subtle way to criticize the world of its time, whether it be for national politics or a war or a culture clash – and the 60s certainly had no shortage of all three of these. It plays into both episodes this week, creating tension in different ways that we’ve seen versions of already this season, but the execution is handled in mostly fun ways.

Shore Leave is one of the more interesting entries in Star Trek so far, but less because of what happens on the screen and more for what conspired behind the scenes. Before creating Star Trek, Gene Roddenberry created The Lieutenant for NBC and barely had a break between the two series. At the insistence of his wife and doctor, Roddenberry took a well-deserved vacation to relieve some stress. Though the script comes from Theodore Sturgeon – a prolific and respected sci-fi writer and the inspiration for Kurt Vonnegut’s Kilgore Trout character – you can see Roddenberry’s fingerprints all over the themes of Shore Leave.

One question inherent in any sci-fi property set in the distant future is how much of our current pop culture and traditions will survive. Will organized religion or secular holidays be remembered the same in 300 years, or will the creatives behind the scenes insert their own takes on how they may shift? It’s evident in both installments this week: with The Conscience of the King, it’s in the enduring appeal of Shakespeare and classical theater, and in Balance of Terror, it’s in the opening minutes as Kirk presides over a wedding ceremony.

There may not be a strong thematic thread evident through each of these installments, but they’re perhaps the strangest collective bunch of the show so far. One deals with an incredibly straightforward premise, and the other’s plot is so memorable and complex that I mostly knew of it from the spoof that Futurama produced.