This blogpost is focused on looking at how What’s Past is Prologue, the sixth episode of Star Trek: Discovery fits into the events and themes of the previously established universe. I’ve written similar blogposts looking at each previous episode (you can read the first here, and a full list under the Star Trek Discovery tag).
Climate Change
The Terran Empire’s toxic approach to the mycelial network is essentially a fossil fuel metaphor. Whereas the Prime Universe crew are conscientious about doing as little damage as possible, the Charon’s mycelial power core poisons the wider mycelial network while drawing power from it. Saru to be shocked by the Terran Empire’s short-sightedness, given that the process means that eventually, in Stamets’ words, “life as we know it will cease to exist”.
This recklessness works as a parallel to the real-world use of fossil fuels. Despite its hippyish idealism, the Star Trek franchise hasn’t touched on climate change and environmentalism as often as might be expected. The most notable exception is the TNG episode Force of Nature – built on the premise that warp engines damage areas of space which have excessive warp travel, an issue which isn’t revisited on-screen. (I’ve read that the reason Voyager’s warp nacelles physically rise before the ship goes to warp is to counter this effect, though I’m not sure whether this is canonical.) The climax of What’s Past Is Prologue implies that this analogy won’t be immediately revisited, but it’s a storytelling device that DIS could reuse in future.
Divergences and Parallels
The soldiers working for both Mirror-Lorca and Mirror-Georgiou have no qualms in vaporising their opponents, as opposed to the iconic Starfleet standard of setting phasers to stun. In addition to these needless deaths Mirror-Stamets – a genius scientist – is executed for no good reason, while Saru is living a life of slavery. Morality aside, the backstabbing approach of the Terran Empire seems to lead to a great deal of wasted talent.
This wastefulness of their own people is offset by leeching off other races. The ENT Mirror Universe episodes revealed that in the ‘first contact’ with the Vulcans in 2063, Terrans robbed and exploited their visitors, whereas in the Prime timeline this was the beginning of centuries of cooperation. Despite this, the Terran Empire of the ENT era didn’t appear any more technologically advanced than the Earth Starfleet of the same era in the Prime Universe. Despite the capture of the Defiant in that story (with technology a century more advanced) the same appears true of this Terran Empire of the 2250s.
Saru’s Speech
In the build-up to the attack on the ISS Charon the difficulty of the task becomes apparent. It would be reasonable under these circumstances to prioritise going home, or to accept the mission would be a noble suicide run. Instead, in the vein of Kirk cheating the Kobayashi Maru Saru announces that “we will not accept a no-win scenario.” He makes the decision to aim for the near-impossible idealistic choice, while persuading his crew that, with enough hard work and cooperation, this is achievable. Making the challenging, idealistic choice, requiring huge skill and precision, rather than making compromises. It’s an encapsulation of everything that Star Trek is.

Transporter Malfunction
In a flashback, Mirror-Lorca reveals that he originally came to the Prime Universe as a result of a transporter accident while on the run, trying to beam through an ion storm. This is the same method that resulted in Kirk’s away team swapping places with their alternate selves in the TOS episode Mirror, Mirror.
Lorca’s plot – pretending to be his alternate universe doppelganger – also has precedent. In DS9’s Through the Looking Glass Ben Sisko is enlisted to take the place of Mirror-Sisko, a rebel leader who has been killed in action.
In a Mirror, Lorca
In a sense it’s a shame that Lorca has been revealed to be from the Mirror Universe – I would have liked to see a moral collapse of a Starfleet captain like Garth of Izar or Ronald Tracey. But the choice the writers made means that Mirror-Lorca is a character whose views are fundamentally at odds with those of the Federation and Star Trek, to an extent that’s only revealed in this episode.
In this episode Mirror-Lorca opines that the transporter malfunction that led him to the Prime Universe was “physics acting as the hand of destiny”, and he has previously told Burnham how strongly he believes in destiny over free choice. Generally the Star Trek franchise has celebrated free choice over predestination, with the most notable exception being the recent Chris Pine-led films. In the first of these films the Kelvin-Universe’s Kirk, having lost his father before he was born, is a drunk and a bar-crawler, whereas Prime-Kirk is described as “a stack of books with legs” at the same age. It’s one of many differences that means that Kelvin-Kirk and Prime-Kirk have lived fundamentally different lives. So the Kelvin-Timeline’s insistence that Kirk ‘belongs’ at the helm of the Enterprise struck me as out of step with Star Trek’s meritocracy – having lived a different life to Prime-Kirk, Kelvin-Kirk isn’t the same person who circumstances and hard work moulded into a great leader.
Lorca is steadfast in his belief in destiny, telling Stamets “nothing that’s happened to me was an accident. Not ending up in another world, not finding a ship that would help me return here, none of it. I’m living proof that fate is real.” It’s a belief that would fit in with the central philosophy of Star Trek XI.
Ironically, despite repeatedly speaking against the idea of free will, Mirror-Lorca’s achievements appear to support them. On the run and in an unfamiliar universe, Lorca not only found his way back, but back to the heart of the Terran Empire, in the process moulding the Discovery’s crew into who he wanted them to be. We know that he brought Prime-Burnham onto the Discovery because he knew her counterpart – the same could be true of Landry, Stamets, Tilly and Owosekun. By sheer force of will Mirror-Lorca made the near impossible happen, and briefly served as Emperor. In a way, this is a dark interpretation of Star Trek and the Federation’s belief in free will – that our future is the future we choose for ourselves.
Geek Banter
After being informed that Saru won’t accept a no-win scenario, Tilly and Stamets discover that it’ll be possible to ride the mycelial shockwave from the Charon’s explosion. As with all Star Trek technobabble banter what’s important isn’t the words (which have just enough internal logic to make it possible to follow) but the camaraderie that underpins it. TNG’s Data and Geordi had a relationship built on similar interactions, while VOY went a bit overboard on focusing on the style rather than the substance of technobabble – the language rather than the warmth. The gathering of the senior crew for Saru’s inspirational speech is one sign that DIS is growing into the mould of what we’ve come to expect from Star Trek, and this is another.

Agony Booths
The agony booths which have appeared over the last four episodes are a staple of the Terran Empire. They first appear in the TOS episode Mirror, Mirror (where Mirror-Chekov is punished after a failed assassination against his captain) and in the ENT two-parter In A Mirror, Darkly. In the latter (set a century earlier than TOS and DIS) Mirror-Reed and Mirror-Phlox are revealed as the inventors of the agony booths, with Mirror-Phlox explaining that the booths “continually shift the stimulation from one nerve cluster to another, keeping the subject in a constant state of agony.”
Nasty.
The Nature of Monsters
A long-time Star Trek staple has been not to judge alien races by their appearances. In TOS both the Gorn and Horta at first appear to be melodramatic monsters until the crew learn that, from their perspectives, they have justifications for their actions. Probably the most overt example of this lesson – not to judge aliens by their appearance – comes in the VOY episode Nemesis, where Chakotay is fooled into fighting for a Human-looking but violent race against a Predator-looking but peaceful race.
DIS has clearly placed large importance on making the Klingons look more alien, more monstrous than either of the previous depictions of the race. But, prosthetics aside, there’s a large overlap in the depictions of the Klingon and Terran Empires. Both have large city ships and confrontations take place in throne rooms, there’s a large overlap in style between the Charon and the Klingon Ship of the Dead. The two Empires share a similar willingness to vaporise their enemies, and even a similar style of lighting, much darker than on the Starfleet ships. What’s important about the Klingons is obviously not that they look horrific, but their actions. Even one of Mirror-Lorca’s phrases – “make the empire glorious again” – hints at language commonly used by both the Klingons and Donald Trump.
One of Mirror-Lorca’s monologues in this episode is such a good counterargument to the Starfleet outlook that it’s worth transcribing in full:
“You know that the Federation is a social experiment doomed to failure. Childish idealism – every species, every choice, every opinion is not equal. No matter how much they want it to be. The strong and the capable will always rise. Like you and me. And every living being is safer and happier knowing their place. That’s why we have a duty to lead. Like what you did that day at the Binary. Stay with me. Stay here and help me bring peace to this world through strength and order, the right way.”
But as concise and eloquent as Lorca’s argument is, there are obvious retorts. There’s no reason to believe that Mirror-Saru will be happier as an unnamed slave and then as food than his counterpart is on the bridge of the Discovery. And the Federation is hardly the absolute meritocracy that Mirror-Lorca depicts it as – Kirk’s opinions have more weight than Chekov’s, and Picard’s have more weight than Wesley Crusher’s.
Despite what Mirror-Lorca argues, Federation Starfleet is not a soft organisation, but a demanding one. The difference between it and the Terran Empire is that where the Empire motivates through fear, Starfleet achieves the same through encouragement and camraderie. Tyrants like Lorca can only rise by constructing a strawman depiction of the other possible political systems, and persuading their more conscientious followers of the lie that their cruelty is necessary.

The Green Dot
After riding the mycelial shockwave back to the Prime Universe a series of blue mycelial spores float in the engine room, before one turns green and settles onto Tilly’s uniform. It’s a weird detail that seems like it will be important later.
In the Wrath of Khan Spock places his ‘katra’ (basically his soul) into McCoy, allowing him to live again after death. Given that Culber (or something resembling him) was able to communicate with Stamets from the afterlife, perhaps this was him doing the same with Tilly. In an episode of TNG an energy being flies into Deanna Troi, impregnating her then living out a life as her child. At this stage either explanation is possible (as are many others) but it will have some sort of importance.
Yesterday’s Discovery?
The Discovery returns to the Prime Timeline roughly nine months after they left, with the Klingon War going badly. There’s a possible similarity to the TNG episode Yesterday’s Enterprise. In that episode Picard’s Enterprise-D pulls an older ship, the Enterprise-C, forward in time through a distortion (there are far too many Enterprises in Star Trek). As a result of the crew of the Enterprise-C not dying an honorable death protecting a Klingon colony, relations between the two deteriorate to the point of war…a war which the Federation is losing.

It’ll be interesting whether DIS treats this as an alternate timeline. Like the Enterprise-C, the Discovery has travelled forward in time, not being present at a point when they could have had a pivotal influence. But on the other hand, Starbase 46 (Discovery’s destination when it moved into the Mirror Universe) seems to be close to the planet Organia. This is a world which in the TOS episode Errand of Mercy will be considered a key tactical site which the Federation and Klingons both battled to control. This seems to imply that Starbase 46 will not last the ten years between DIS and TOS, so maybe Klingon forces will push back the Federation border. It may well be that Federation defeat – though not absolute – is the new normal.