This is the official lore of the Half-Life 2 modification "Entropy: Zero" and is written by the developer of the game, but has been modified to fit a proper entry for the wiki, mostly grammatically.
Last revision: 6th of April 2017.
This is just a short summary of the whole story below and does not include some critical data required to more advanced understanding of it.
Eleven months before the events of Half-Life 2, and unbeknownst to the rebels of the underground, the G-Man was preparing City 17 for an uprising. He needed to ensure that weapons and appropriate supplies would be available to rebels at a moments notice of rebellion. Eli Vance and Isaac Kleiner also required some very specific Combine technology to finish their work on their teleportation devices. This was key.
The G-Man achieved this by reaching out to the rebels hiding in the abandoned remains of City 10 and orchestrating their actions to assist him. Their involvement ultimately led to their deaths at the hands of a single Civil Protection Unit, and brought an end to the City 10 sanctuary.
Pre-Player Arrival Edit
During early Combine rule, City 10 was established as a medium-sized urban centre located north of City 17. In terms of Combine development, the city wasn’t really used for much, but it provided a direct railroad link to City 17. Because of this, City 10 was used mainly as a staging and overflow area for City 17.
City 10 was overseen and managed by a mini-citadel type structure called ‘Pillar 10’. Pillar 10 acted as a remote unit production center, and produced reinforcements to the Combine controlled northern regions.
A whole two years before the events of Half-Life 2, City 10 was ravaged by a deadly viral outbreak that came to be named ‘CFLU’. The Combine were more susceptible to begin with, as the virus primarily targeted the genetic structures used to bind their augmentations to their brainwashed prey. Over time though, the virus adapted to infect and kill unaugmented humans as well. This caused a violent upheaval in City 10.
The Combine knew they’d have no chance of suppressing citizens in City 10 with their units being wiped out by the virus, so they opted to leave and merged with the forces of neighbouring cities. All infected citizens and Civil Protection Units were killed off. During this time, Pillar 10 was equipped with sustainment devices to keep the infected units inside structure healthy enough to continue Combine enforcement.
Citizens given the all clear were relocated to City 17. This was a lengthy process that lasted months, with many citizens being shifted from one city to another over long periods of time. Gordon meets some of these people as he arrives in City 17.
Everything came to a halt though, when a small rebellion started. A lot of Civil Protection Units were against the idea of being put to death and changed their allegiance. They worked with rebels to fight against the Combine in an attempt to secure the city. Ultimately many Combine units were killed and eventually they opted to ditch the remaining citizens/rebels and shell the city. City 10 was written off, but a large group of rebels survived.
With the aid of the next winter, the rebels found that the CFLU virus appeared to be suppressed by the cold weather. During this time they took preventative measures and established a foothold away from infected territory. Using Combine munitions, they blew large holes into the subways and tunnels below the city and dumped the infected corpses. This kept the virus underground and away from their sanctuary.
During the intervening months, the rebels in City 10 connected with the citizen railroad in City 17 and a supply line was created. City 10 was looted initially for Combine weaponry and equipment. Over time, escapees were led away from City 17 to the secret sanctuary of City 10. Barney led some of these escape parties and became thoroughly involved with the rebels of City 10.
Thanks to a rebel named Laszlo, the rebels hiding in City 10 managed to create an algorithm that would allow human technology to interface with Combine technology. This allowed the rebels of City 10 to turn Combine turrets friendly, among other things. The sanctuary became a fortress and before long the whole city was wired against the Combine.
The Vortigaunts were very interested in Pillar 10 - the mini-citadel hosting the city. They were able to use Laszlo’s knowledge to gain entry to the structure. Using their own energies, the Vortigaunts kept Pillar 10 alive as a ‘zombie-citadel’. They expressed extreme interest in the device powering the structure - a device known as the ‘Quantinode’. The Quantinode utilised an unknown science of ‘zero entropy stasis technology’. Laser arrays in the structure were focused onto a singularity that siphoned heat energy from its surroundings to create a sub-zero fusion reaction to power Pillar 10 and the Combine technology throughout the city.
The Vortigaunts in Pillar 10 also kept the giant pistons in the structure from stopping, to prevent antlion infestation.
For a time, City 10 was a safe haven for escapees.
The G-Man's involvement Edit
All of this caught the G-Man’s attention. He saw an opportunity.
The G-Man reached out in secret to the leader of this now, very large group. He offered to keep the rebels out of harm's way and also offered water and food. In return, the rebels would continue to push weaponry and equipment back down the railroad to City 17.
Whilst it was easy at first (due to the abundance of Combine equipment in City 10), the orders became harder and harder to fill. The rebels of City 10 had to venture further and further out to find requested items and handfuls of people had died. It wasn’t long before equipment stopped arriving in City 17.
The G-Man approached and offered their leader one final chance at redemption.
He ordered the leader to have his rebels derail an important Combine train that would soon be headed for City 17. The train was set to pass through City 10, and carried salvaged equipment from Black Mesa. It was the perfect opportunity to score some major gear from the Combine, but more importantly there were some highly valuable and much needed technical items aboard that needed to reach two famous scientists hiding in City 17 - Eli and Kleiner.
11 Months before the events of Half-Life 2 Edit
Combine forces in an unknown area of woodland - far from Combine control, perform a raid on a countryside rebel hideout. Inside they find some old Black Mesa salvage destined from White Forest before the invasion. This is loaded onto a train and hurried back to City 17 with great importance.
The rebels prepared and then committed to derailing the train by collapsing a road tunnel running above it. The lead rebel - following his gut feeling - sends Laszlo and several others back to City 17. Barney declines and opts to stay for a while longer. Laszlo leaves in the dead of night, as the train as derailed.
Almost all of the Combine units onboard were killed in the crash. The survivors were dragged and tossed into the zombie-infested tunnels below City 10. The equipment the G-Man requested was passed immediately down the railroad.
A day later, reports reached the main hideout that a lone Metrocop was loose in the city and was killing the rebels. The leader of the rebels locked himself in his quarters and refused to leave, putting the rest of the rebels on edge. Barney tried to negotiate with him, but was unsuccessful. The rebels didn’t have much time to consider this though, as their turrets suddenly turned against them.
The rebels of City 10 were caught off guard and suffered tremendous losses because of this. A large group banded together inside the main hideout and attempted to kill the Metrocop. Miraculously, they failed and were wiped out.
Whilst the hideout was under attack, Barney set a trap by posing as a captured Metrocop. The Metrocop destroyed a stash of weaponry the rebels had obtained from the train, and discovered the carbonized remains of the rebel leader. He then freed Barney - believing him to be an ally. Barney timed his moves, put a bullet in the Metrocop’s back and knocked him unconscious.
Knowing he’d die, the rebels of City 10 decided to throw the Metrocop into the tunnels beneath City 10, and left him for dead. The rebels then burnt the evidence and their hideouts and abandoned City 10 for good. They headed in the direction of White Forest.
The Metrocop however, survived the fall, with bodies cushioning his landing. He moved through the tunnels and subways looking for a way back to the surface. After fighting through zombies, unbeknowingly contracting CFLU and investing in the aid of a latent Stalker, he reached a Combine bullet train which took him directly to Pillar 10.
The Metrocop eventually gained access to Pillar 10, even besting the Vortigaunts working there. He discovered that the Vortigaunts had been meddling - they were trying to get synths to work for them. It then became obvious that the Metrocop had contracted CFLU during his time in the tunnels, however he managed to use the sustainment devices in Pillar 10 to continue his conquest. Inside, he was able to divert power to the main terminal and elevators. After reaching the main core terminal, he fights the lead Vortigaunt.
The fight is ended abruptly when the Vortigaunt triggers an Entropy Conversion Event, which freezes Pillar 10 in solid ice. The Metrocop and everything in the surrounding area is frozen solid in an instant in a stasis event.
Much later beyond the events of Half-Life 2, Advisors find the frozen remains of the metrocop. They playback the mask cache recording and witness the actions of the Metrocop and how far he was willing to go to alert Overwatch. This impresses the Advisors and they communicate with him their intentions to preserve his consciousness.
An apparatus comes down and cuts into the Metrocop’s mask and face. He screams. The game ends.
They replicate his consciousness and beam it down to latent Combine soldiers.