The Great Frost itself. Scientists across the globe try to find the cause (and possible ways to reverse it), since the catastrophe seems to deny the very concept of physics. Even with all the factors from ash clouds to the Sun dimming, it should have been impossible. Then a theory about The Saffron Cloud appears, forbidden to even talk about by the pre-Frost governments, a chemical/climate-altering weapon of mass destruction. The preparations were originally made "just in case" (i.e. there was a possibility it wouldn't happen), before the Frost came over the course of weeks. How much of the current Crapsack World state was really caused by nature, and how much by the human factor?
In the city the population - barring some potential American refugees from Tesla City in A New Home - is entirely white British. The reason for this is found in the lore. As the temperature dropped and it started to snow, the first places to fall to the frost was the southern equator. Unprepared for heavy snowfall and the waves of refugees from Europe, the southern parts of the planet fell into disarray and eventually fell silent. It’s implied throughout the story that your region is possibly the last inhabited one left on Earth, and until the expansions came out, that your city may be the last.
And that's not even getting into that, from a genetic standpoint, human population must be at least several hundred strong to even have a chance at survival. If you survive at the cost of human lives, you can end up below the minimum level of 500, which means that if the cold does not kill your descendants, the inbreeding will.note The human population presuming pristine and deliberately varied genetics can actually go as low as 8 theoretically and still be viable. Now granted in this situation we don't have pristine genetics or deliberate selection for diversity, but presuming some assortment from different districts of London with different genetic backgrounds such as having some level Greek ancestry, African ancestry, Asian ancestry, Celtic ancestry, and some other varieties of European are mixed into the gene pool that could easily drop the required number to one or two hundred. Given this story takes place with London having been at the relative height of its Imperial Age, this is quite likely as London was both a center of commerce as well as having relatively recently had settlement from the Mediterranean world at least in terms of genetics.
If food runs scarce, you get the option of passing a law to eat the dead. It's a rather long chain of events starting with food riots, then starvation, then your guards catching cannibals in the streets, and then people storming the cannibals' hideout - even your guards requesting permission to intervene are not sure if this is a lynching of the guilty or an attempt to get some of the meat for themselves. At first you simply allow covertly cooking dead bodies (or, if the relevant law is passed, using them as fertilizer), and then people will do it themselves. In the Frostlands, your scouts can find not one and not two sites where entire settlements have fallen because of this.
The final storm. First you get the warnings from your researchers. Then you see it in the distance, a wall of deadly cold taking the entire edge of the map, rapidly approaching your city, consuming map locations one by one as they become too cold to get into. And then "The City Must Survive" starts playing and your battle for survival begins.
The Purpose paths in the Book of Law. Both involve giving your citizens something to believe in (unity in purpose and toil in Order; connection through religion in Faith), and in both cases, people are slow to accept it. Faith, in particular, is a slow boil, and it takes several days before the City has any amount of religious followers. Order immediately has supporters, but also dissenters who know all too well how authoritarianism starts - and then the nightmare fuel happens. The scary thing isn't that both paths take you to totalitarian dictatorship; it's that your citizens demand it. You don't force any of the Laws; the people do, and they will violently and gruesomely murder dissenters who saw the red flags. They will want propaganda, patrols, excommunications and inquisitors, and will hate you for not giving it to them. In keeping Discontent low and Hope high, you may feel forced to follow the people's demand and create their New Faith/Order - or you can stand your ground and see your city tear itself apart. Authoritarianism doesn't come from one person; that's just how it starts. It comes from all of us.
Some of the things your citizens start to do whenever you start signing harsher laws under Faith or Order, particularly in The Refugees. If you sign Public Penance, a lynch mob will proceed to march a good 20 Lords, in the nude, to a gallows in an attempt to lynch them. You're helpless to stop this unless you have Faithkeepers/Peacekeepers...
Once you sign New Faith or New Order, a quarter of your people immediately see the red flags and protest against the signing of it. If you decide to go through with it, these protesters are all either killed or converted back to your cause by force. A brief pseudo-animation plays of people being dragged away, beaten, and murdered, before one such soul is unlucky enough to be put on an steam-powered execution platform to be boiled alive. Oh, and you can now do that once every couple days, just in case it wasn't already clear how nasty things are getting.
What is the preferred method of public execution in this game? Chain a half-naked person (when it's -80 Celsius) to a scaffold and boil them with overheated steam from the generator. If you never embraced the New Order / New Faith, in the event of a mutiny you will simply be cast out of the city: your people do not want to kill you, and simply banish you into the Frostlands, in recognition of your genuine attempts to make things better for everyone. However, if you established the executions, they will drag you to your own invention and kill you in your own signature way. And it does not happen offscreen; you even get to hear your character briefly cry out in agony before the Game Over screen comes on, displaying their (still lashed to the platform) frozen corpse.
If you follow the Faith path, several events will appear involving the public flogging and/or execution of heretics and sinners. You would expect an option to spare them (i.e. stop the lynching) which you always had before... Except your Faith Keepers will outright refuse to save the filthy sinner, stating that people are doing what is right.
In a setting where being too humane can spell doom for your people, you will have to revert to options that the game considers evil, mocking you for becoming a tyrant even if you never used those... Just because you even considered them. Even when you had no choice, even if you tried to apply only the minimum amount of force and persuasion, even if you were honest to your people and mildly punished only the absolute worst of arsonists and murderers - history will remember you as a bloody tyrant who abused Order or Faith and exploited child labour.
Even worse, apparently this was the canonical path. Your outposts in the latest expansion outright say New London rules them all with an iron fist, and are willing to take any opportunity to break free.
The description is similarly ominous when paired with some of the remarks in the trailer. The mentioned accusations of "Abandoning our brothers" and "Abandoning God" sound awfully familiar, don't you think? note Specifically, these lines can be speculated as referencing the Refugees scenario and going down the Faith/Order pathways, perhaps with the addition of desperate measures such as cannibalism becoming covertly allowed due to a lack of food. In either case, the implication is that the unnamed settlement left at least some of their people out to die in the Frostlands, then went completely down the Faith/Order route until the citizens revolted, killed the Overseer, and presumably died or abandoned the city.
You think you know cold? -150 Celsius. For comparison, not even Mars gets temperatures that low. It freezes soil, sends people to infirmaries in droves, and many will be found dead in their beds afterwards. As the sky darkens, more and more people will beg you to let them leave their posts to be with their families in their last moments or at least pray before they die... Which you can forbid,plummeting their hope even further down.
Almost no other experience in all of gaming can inflict the same kind of leaden, overpowering, soul-crushing despair on a gamer as the climax of the A New Home scenario on their first playthrough if they didn't manage to master the game extremely quickly. If your preparations were inadequate for the unprecedented challenge of the Great Storm you will be forced to watch helpless as the temperature goes down and down and down and just when you think it can't possibly get any colder, it does. Your mines freeze over, your workplaces shut down, your coal and food reserves dwindle, your houses become tiny freezers, your infirmaries overflow, hope falls, discontent soars, your citizens begin to die, first one by one and then in ever-increasing droves, and the generator gutters and dies as, unable to do anything else that will make a difference, you desperately pray that the dawn will come before the last life is extinguished. Not for nothing is Frostpunk considered the most gut-wrenching city builder game ever made.
The story and fate of Tesla City and its inhabitants fits this description. Led by a despot who valued his citizens only so far as their usefulness to the city, workers and engineers and children who were no longer considered useful - such as the sick and the amputees - were either exiled into the Frostlands or left to die aboard the ship they arrived in. Nearly all the exiles themselves slowly starved to death in the icy Frostlands, but the city itself ended up faring off far worse, with nearly the entire population being electrocuted to death or forced to leave when the Generator was completed and turned on.
When your scouts find Tesla City, it is described as there being charred bodies lying in the streets and the stench of burned flesh lingering in the air. Furthermore, your scouts see lightning streak from a tower, hitting a building and leaving a gash in its roof. The Teslaites never stood a chance inside that human bug-zapper. At least your scouts manage to turn it off... Except there is a 50% chance they will do so at the cost of their lives.
The Fall of Winterhome:
The scenario begins with your city in ruins and a good 15% of the population dead. You know your predecessor was an idiot and that he didn't go down without a fight... But burning over 90% of the settlement appears just a massive final defiance on his part, which makes you ask just how horrible his actual rule might have been that people were willing to risk THAT to get rid of him.
If you dig a child out of the burned rubble, an event will tell you that the child will die without immediate care that you can't provide. There is a chance of him surviving if you have Infirmaries running (or medical posts with radical treatment, though that can leave them as an amputee) and with space for them in time.
No matter how good you are, you cannot save everyone. The Dreadnought is limited to 500 people, meaning that someone in your 600+ people city WILL die. Either you kill them off deliberately trying to maintain order, or the engineers keeping your Generator stable will be left behind (possibly with you, if you choose to not abandon them in the darkest hour).
The engineers, at one moment, will ask you to let them on the Dreadnought ahead of time, at the cost of abandoning more people in the doomed city. If you refuse, they will rant at you to not be surprised if the Dreadnought just stalls in the middle of the Frostlands. While this seems not to have occured (presumably due to the captain heeding their advice, due to you finding no Winterhome engineers in "A New Home"), this is still no guarantee of their survival.
You have an option to launch the Dreadnought while incomplete, either without enough supplies or with too little space, or just before people actually get aboard. Even worse, it seems that this is what canonically happened: You find a few dozen kids in the gloomy cave in "A New Home", along with mentions of the dead adults that got them there. This means that the kids were not fully evacuated before the last generator malfunction, meaning the entire effort was running less efficiently due to demoralization (unless the captain lied about another city, then killed off the engineers that threatened to reveal it.) You also find some workers, and yet more kids, in Freshwater Springs. This means that the captain allowed (or was unable to stop) panicked mobs from fleeing the city in one way or another. This also means that an equal number was left behind to die. This, along with the amount of corpses found by the scouts, from the graves in the frozen grove to the dead of Winterhome proper, means that the canonical ending is quite far indeed from the Golden Ending. The only glimmer of hope is that while the evacuation did not reach total success, it also wasn't a complete failure, as implied by New London finding no trace of Winterhome's dreadnought being in ruins in either of the scenarios that follow it in the timeline meaning that people were evacuated. Sounds great at first...and then you realise that the Great Storm is about a month away and the refugees have no idea about about the city they just missed out on.
Refugees:
If you don't welcome the Lords then they will surely die. Either you build expensive guardhouses and they leave to freeze to death in the Frostlands, or your people go to their camp and slaughter them all. The fact that makes this nightmare fuel is that a large number of the Lords are just children. Their innocent blood is on your hands for rejecting them.
Most of this scenario is spent creating a free city of like-minded working men and women, and division isn't a big deal. Then you see the marker for "The Lords" slowly creeping towards your City on the map... Subverted in that, while the Lords are a bag of dicks, they're not armed and don't intend to force the Refugees out of the City; they just want to live there. They're still a problem, but at least not one that is as terrifying.
Even more so with Lord Craven. A name like that is truly fitting for a final boss! Which he sort of is. He did do horrible things in London, but by the time he reaches the City, he's depowered, afraid, and only looking to save people. The challenge he brings is actually that your own people will want revenge for his deeds...
The Last Autumn:
Worksite accidents tend to have huge explosions, happen without warning, and inevitably result in massive injuries. Workers caught in the accidents can be heard screaming in pain - they will be injured and likely crippled for life. While the 19th century was by no means the best time in regards to work safety and regulations, these accidents are of horrifying scale... And it's up to the player whether to introduce safer conditions which completely nullify these accidents (and risk falling behind schedule), install safety equipment in case of an accident (which costs valuable resources) or just send people into mines full of toxic gas and let them die in fires and explosions, knowing full well of the potential losses and broken lives. And what's worse is that it's all justified: not meeting the goals means freezing to death for both workers and future refugees.
A few events warn you of foreign spies and agitators trying to undermine your construction efforts: from spreading propaganda about labor unions to outright instigating arson. Even in the face of extinction, the great empires can't seem to stop fighting among themselves.
The cold, stern tone of your superiors' messages, in which they show just how little the IEC cares for its employees. They just tell you calmly how bad things really are (which you keep your people from learning, even censoring their letters) and cold-heartedly describe how other Generators fail one by one. To them, death is nothing more than a statistic... which is a feeling some players may experience after playing a few scenarios on their own.
Assistant engineer Euphemia "Effie" MacLachlan who appeared in the cinematic can later be found at what's left of Site 107 and will join your crew. The Generator exploded, killing nearly everyone on the site and making Site 113 the only hope for Liverpool. She was there, she warned them it might happen, she begged the Sitemaster to install precautions, and yet nobody listened because, apparently, she was too young to have their ear. Now you see before you the consequences of ignoring the pleas of the engineers.
A more disturbing implication (although the player has to deliberately invoke it to apply, and this was likely not intended). In the main game, House of Pleasure is a measure not encouraged in any way, and building it (hell, even considering to build it) will result in a drop of Hope. In the Last Autumn, it has no penalties other than a few health risks, and your workers honestly see nothing wrong about having it on site. For it to work, you need five volunteers. You don't just invite women from London, no: you order five of your employees to do it. Can be even worse if you sided with one class and order ladies from the other to participate: either your Engineers will enjoy the company of the oppressed class, or your workers will get revenge on the once-privileged Engineers in one of the worst ways possible.
The Automatons are not available in this scenario. You would probably expect the signature technological marvel of the British Empire to appear in the prequel, considering the importance of the Generators... But you have to deal with all this the old-fashioned manual labor way since (officially) it's just cheaper and the machines are too valuable to risk using them in such dangerous work. Then an off-hand mention comes in a letter, stating that mechanical walkers were used to fire upon the crowd during the riots. The life-saving machines that your people in New London saw as their angels of hope were never tools of salvation: they were weapons from the start. Your engineers in The Arks can optimize the production of the Automatons by removing the components "reserved for future expansions", without mentioning what kind of expansions those were... Well, now you know the answer.
trailer begins fairly optimistically, showing an apparently-thriving city ruled over by a benevolent leader, only to transition halfway through to the same city - only now visibly darker and grimier, with the ruler about to face execution by the steam-exhaust method seen in the Faith/Order path. We're then treated to a lovely display of just how nasty this method is, with the captain audibly shrieking in agony as the superheated steam boils him to death. The trailer then ends on a final pan across the city, now frozen and desolate beyond the leader's frozen corpse (still chained to the Generator's execution platform), heavily implying that the citizens may have doomed themselves by executing their captain.