The first season of Star Trek: Discovery is drawing to a close, and after Sunday night’s penultimate episode, it’s time for us to start assessing the season arc as a whole. In many ways, this season will ultimately be defined by the long detour we took through the Mirror Universe. All the many subplots and character transformations come back to that or function as echoes of it.

For now, let’s set aside the question of whether the Mirror Universe episodes were good and focus instead on narrative mechanics. What does the presence of the Mirror Universe do to our story? How does it change the stakes?

Spoilers ahead. If you read further, your eyeballs will boil with plot reveals for every episode that has aired this season. Don’t do it unless you are ready.