Ode to the City Primer

The date is Feb 6, 739, and for the residents of Sigil, it may as well be the end of the world.  Sigil, also known as the city of doors, is a bustling metropolis built on the inside of a giant torus floating above a mountain in The Outlands, and it is a mere shadow of its former self.  For centuries, there had been some magic causing doorways within the city to randomly connect to other seemingly random locations throughout The multiverse.  Most often these places were cramped and forgotten, out of the way, or otherwise simply not in the public eye.  One could have easily been exploring an old abandoned building, hiding in an old wardrobe, or even fallen down a chimney only to find themselves suddenly within the city of Sigil, a magical place unlike any other where people of all sorts, living or dead, would come to gather, share information, peddle their wares, or simply as a convenient passage from one place to another. 
The change was not completely without warning, and in hindsight most residents agree that this fact is actually to their detriment.  It all began on April 28th, 719.  Sapient creatures of every walk of life throughout The multiverse had a shared vision of a unicorn by the name of Izar, presenting a plea for help: reality itself was under siege, according to Izar, by strange otherworldly entities known as the Forms.  These forms are, in essence, abstract concepts given an enormous amount of power over the shape and events of The multiverse.  The residents of Vigrid, which would later become known as the Einherjar, needed help to prevent The Age of Mortality from ending in the death of every known god. 
This resulted in both a mass exodus and a mass ingress - residents of other planes fled the city even as Sigil natives and scholars from every plane came rushing in to meet and agree on a plan of action.  The city council consisted entirely of representatives from the Outer Planes, who all returned to their homes to gather what information they could and return for an emergency meeting.  Unfortunately, the council never made it back.  On April 30th, 719, just one day before the council was supposed to return to the city, was Ragnarok, the battle between the gods and Iapetus which brought The Age of Mortality to a close.  On the surface, this should have been good news.  It wasn't.
As soon as Iapetus fell, the age changed.  The wheel turned, and Mortality itself no longer held sway over The multiverse.  At the same time, however, a new Form moved in.  It is still unknown what the current age is, or who the new Avatar is, but when the wheel turned the portals connecting Sigil to the other planes all closed at once.  The city was unmoored - Residents were stranded outside of the city, while visitors were stranded within the city.  The city council, now unable to return home to govern, could no longer serve to rule.  Chaos reigned, and continues to reign even 20 years later.
The Window, formerly a cartography guild, suddenly found itself to be the only organization that possessed both the manpower and the prestige to effectively rule the city.  What agents they had that were not trapped outside of the city immediately sprang into action as volunteer disaster relief, and over time The Window gradually became the de facto rulers of Sigil.  Ostensibly the council still writes the laws, but with their members unable to return home they can only communicate through the Sending spell - enough to communicate, but not enough to lead effectively.  Most of the city watch resigned their posts and took positions with The Window instead, seeking only to do whatever they could to keep the house of cards from blowing over in the wind.  On June 17th, 719, the council finally caves in and declares martial law, to be enforced by The Window, until such time as the portals can be reopened.  This state of affairs has held even to the current day, and it is still an open question whether or not The Window will willingly give up their power once things are brought to normal.
At first, the new leadership spent its time organizing the people, rationing food, and leading research into opening up the doors again.  As time went on, it became increasingly clear that opening the doors would not be a simple task.  In fact, it would be impossible with current technology.  A portal could be opened, only to close again within seconds.  Creating a new portal with the exact same symbols would lead to a completely different place.  There was no predictability to it, no stability, no way to keep a portal open for long enough to be used.  The city of Sigil was not self-sufficient, and found it no longer had the means to support its population.  Food and drink were simple enough thanks to the use of magic, but many other things once taken for granted were now hard to come by.  Good booze.  Ink for the quills.  Metal, paper, and fabrics.  The essentials life gradually became more and more difficult to come by.  As tensions rose, old conflicts began to resurface and boil over.  Racial tensions between the Kenku and Aaracokra grew violent.  Wealthy districts began to face looting and riots.  As the people grew desperate, even currency became difficult to come by.  Copper and silver coinage was being smelted down to serve basic needs, while gold began to be hoarded by the rich. 
The Window did what they could, but they could not save everyone.  Gang warfare began to break out, the sick began to die without the proper treatments, and increasing desperation led to even more violence.  It was clear that the city was dying, and all that could be done now was to string matters along as much as possible.  All of this changed, however, when a particularly prominent member of The Window made an announcement.  She was Aria, conduit of hope, and she had inherited a golden music box from her mother.  This box, she said, could bring her consciousness back in time.  She would go back to The Age of Mortality and find a way to save the city or die trying.  When she used the box, her body was placed into a magical coma.  Her body, said Aria, could be used as living proof that the city would survive.  If she died in the past then her body in the present would die as well.  If she had to give up and try again, she would awaken from her coma.  For so long as she remained asleep, that meant she was still fighting to save her people.  Aria was an extraordinary speaker, and had a flair for the dramatic - after entering her coma on July 29th, 719, she had herself placed in a glass coffin and suspended in the center of the city.  From here, she reasoned, any resident of Sigil need only look up in order to have proof that this, too, would pass. 
Whether or not Aria was responsible for what came next is still up for debate, but later that same day a salvation of sorts came to Sigil in the form of two gods - The Traveler and Penguin.  The pair traveled to the city (in person no less!) and, with great effort, managed to enchant a single door, The Wandering Door, which could form stable portals... sort of.  It automatically opens to a seemingly random location, closes again in two or three days, and then eventually reopens somewhere else.  Penguin left behind a pit fiend by the name of Izzik to guard the door and keep it running, but the devil seems to have no real control over the door itself.  On a couple of occasions, when the door quit working for months at a time, Izzik would contact one of the two gods who would come and conduct repairs.  He also maintains strict control over who is and is not allowed to pass through the door - operating under orders from Pixo, leader of The Window.
The Window sends a team through The Wandering Door whenever it opens, and they gather as many supplies and as much information as possible before returning to the city.  Due to the unpredictable nature of the door, it is up to complete chance what kind of materials are brought back.  Even so, it has been a great boon to the city.  That door is the single thing preventing the entire city from going down in flames, and the people who go through the door and come back alive are widely regarded as heroes and saviors.
You are not those people.  You do work for The Window, but you are mere peacekeepers, trying to maintain some semblance of order in the city.  The task is not truly to enforce the law, as such.  Instead, your goal is simply to try and keep as many of the residents alive as you possibly can, for as long as you possibly can.  Some days this might mean helping with a disaster, and other days this might mean stopping gang wars, and other days it might mean mediating disputes between powerful people.  It can be a thankless job at times, but remember: This city will live or die thanks to your efforts.  Let's Survive.