The Outbreak covers the events of the original Killing Floor mod, Killing Floor: Uncovered, Killing Floor, and Killing Floor: Calamity. It details the events surrounding the unleashing of the Specimens from Horzine's various laboratories, and the survivors of the initial devastation.
This is largely pieced together, and you are free to not take it as canon if you wish.
Ground Zero
London, in the near future.
The British Government has tasked Horzine Biotech with creating a super soldier. Horzine has their hands in a lot of projects, from weapons development, to robotics, to genetic manipulation and mutation.
Combining the vast resources of Horzine with some technology secretly provided to CEO Kevin Clamely by a World War II German Scientist named Dr. Hans Volter (who had kept himself alive with various experiments), Horzine was able to take the first steps in their super soldier project.
Desiring to bring back his deceased son, Kevin Clamely used him as the genetic base for their first attempt, producing a fleshy clone later designated as a Clot. While the Clot itself wasn't able to fulfill the goal of creating a super soldier, it did provide them with a baseline to move forward with. Especially with how quickly and easily they could produce more Clots.
They began modifying the Clots in different ways, creating new variants through testing and prodding. The Bloat, the Crawler, and so on. The secret labs and projects were scattered all over Europe. Beneath his ancestral home in Germany, Dr. Volter's experiments with butchering and skinning the Clots eventually created the Gorefast, a creation he was more than happy to send back to Kevin Clamely for production in England.
In the Wyre Forest, an underground Horzine facility began a project of their own. Creating a line of female clones (thought to be based off of Kevin Clamely's daughter Rachel due to the ease of cloning her dead brother) they experimented on them with radical new technology allowing them to cloak themselves from plain sight. Called the Stalkers, they were kept in a dormitory with UV lights always on, and a double-sided mirror allowing scientists to always monitor them from behind the safety of the glass.
Horzine's experiments didn't stop with the clones, though. They also experimented on volunteers to see what mutations they could manifest in living humans. They even went so far as to kidnap random people, some for experimentation and others as victims for field testing their creations.
The ultimate weapon they managed to create was the Fleshpound, a monstrously large mutation of a Clot, pumped with stimulants and adrenaline and armed with whirling blades on their fists. Unfortunately, their rage proved to make them too uncontrollable, even with a device implanted into their chest to administer sedatives to try and calm them back down.
Eventually, Kevin Clamely came to see the cloned specimens (or "Zeds") as his own children. They were after all made from his children. He no longer cared about completing the government contract, now he wanted his children to replace humanity as the dominant species on Earth.
With so many shady experiments and activities going on at the various Horzine laboratories, it was inevitable that there would be accidents and some leaked information. Occasionally a Zed would escape and wreak havoc until it could be recaptured and contained. Reports of monster sightings began to spread all over Europe, though most dismissed the claims.
In one facility, a Fleshpound is injected with a new experimental serum, but it unfortunately causes it to go berserk and break it's restraints, killing everyone it came across. It is unknown if it break other Zeds free or went on a rampage on it's own. It's speculated that this Fleshpound may have become the King Fleshpound.
Disguised reporters investigate one Horzine facility, accidentally releasing the specimens from their containment. The escaped zeds, went on a murderous rampage, possibly being the true beginning of the outbreak.
It's also possible that Kevin Clamely started the outbreak himself, as it would have to happen sooner or later for his plans.
Regardless, we know that the main outbreak begins at an underground Biotics Lab beneath a Horzine Office Building in West London and that it likely occurred right around Halloween.
The Response
The Zeds swarm over London, killing thousands. Survivors don't know what's happening and believe everything from an alien invasion to the zombie apocalypse. Panic is everywhere, and only a few are able to stand up to the horde.
Several military teams, one including Private Schnieder, is immediately sent by the British government to the site of the outbreak. Knowing of the failed contract they had with Horzine, they aim to put a stop to this and cover up any connections to them.
Unfortunately most of the teams are killed by the Zeds. Schnieder is the only survivor from his team, and he attempts to make his way through London alone.
Meanwhile, another team closes in on Kevin Clamely himself. In order to delay them, he seals himself within a secret laboratory with his most loyal employees. There he has them use all of their known research to turn him into the ultimate weapon. Robotics, mutation, cloaking, he has it all. Kevin Clamely becomes the Patriarch and kills the entire team after him as he makes his escape.
The Patriarch then proceeds to go around and unleash the specimens from labs hidden all over England. Chaos ensues.
Survivors scramble to get away from the horrors. Some fight back however they can. Traders are able to set up a bounty system where survivors can earn Dosh for killing Zeds, which can then be spent on weapons. With limited equipment, the thought was that whoever was better at killing Zeds and earning Dosh was more worthy of having access to the rarer weapons. One particular Dosh-loving survivor named Mr. Foster was quite adept at killing Zeds and making money, despite having previously worked as a day trader.
The various mercenaries began working together, forming a resistance to the Zed horde.
The Disco Death March Massacre
Every Halloween a massive underground rave is held in an abandoned asylum, called the Disco Death March. This year they had a long list of DJs lined up, including DJ Scully. It was outside of London, but unfortunately for the party-goers a Fleshpound (possibly the one that broke out after being injected) shows up to crash the party. It's unknown if he was housed in a facility nearby, or if he was just attracted to the noise and neon lights. The screams and sounds of grinding metal were drowned out by the loud techno music being blasted in various stages around the asylum. The Fleshpound moved from group to group, killing all he encountered.
Somehow DJ Scully managed to survive and escaped back to London. He encountered a team of mercenaries who were fighting against the Zeds, and informed them of the massacre. They all returned to the asylum to look for survivors. Unfortunately they were few and far between. The only other known survivor besides DJ Scully was a man named Mike Noble, who had attended the event wearing a skeleton costume.
The Wyre Forest Slaughter
As the Outbreak is occurring in London, deep in the Wyre Forest the Stalkers manage a breakout of their own. Sick and tired of the twisted torture and experimentation performed on them, they break out of their UV dorm by smashing the two-way mirror and attacking the observing scientist. From their they proceeded to kill everyone in the facility.
After that, they escaped into the woods, eventually joining the Patriarch's army.
Heavy Metal
Another Horzine facility is discovered hidden inside of their Steel Foundry. The building had been abandoned for some time when Horzine had purchased it and built their facility secretly on-site to hide it from prying eyes. The foundry itself was restored to working order, and employees were hired at various generous rates to work the foundry and ignore anything else they may see.
Now, once again deserted, a team of mercenaries arrive to investigate the facility and see if they can discover any weaknesses of the Zeds.
Fighting Back
Weeks go by as the fighting continues. The mercenaries become better organize and deploy all over England to keep the Zeds at bay and rescue survivors.
Many missions are taken in many different exotic locations. Sometimes they would encounter the Patriarch himself, but even when defeated he would still be encountered somewhere else later on. This lead to some mercenaries speculating that the Patriarch had managed to clone himself as well.
End of the Line
Eventually, three months after the initial outbreak, the mercenaries learn of the Patriarch's last stronghold in England: a secret facility hidden beneath a subway station.
A team of mercenaries arrive to put an end to Kevin Clamely once and for all, by killing him and detonating the reactor in his base. Unfortunately for them, after breaching the facility they learn that the Patriarch immediately escaped to Paris via the trains. Still intent on destroying his reactor, they are guided by Kevin Clamely's daughter Rachel as she sits in the control room.
After setting the reactor to explode, the team has the misfortune of being ambushed by not one but TWO clones on the Patriarch. The team manages to prevail despite the odds being stacked against them, and defeat the two Patriarch Clones and board their own train to Paris to pursue the Patriarch.
Little did they know that this was only the beginning.