Killing Floor

Killing Floor is a co-op survival game from Tripwire Interactive, based on the Unreal Tournament 2004 mod of the same name. Since the first release in 2005, the mod version had its fifth and final official update in 2008. While there was still development work done for a next update on the mod version, on March 2009 an announcement for a retail version of the mod went live. Tripwire Interactive, with the help from the original mod-team, is the developer for this Steam-distributable game. Tripwire is best known for their WWII simulation first-person shooter Red Orchestra: Ostfront 41-45, which also originates as a modification for Unreal Tournament 2004.

In 2008, mod leader Alex Quick contacted Tripwire in order to negotiate the porting his mod to Red Orchestra and distribution of it via Steam, similar to what Tripwire had already done with another Red Orchestra mod, Mare Nostrum. The staff of Tripwire found Killing Floor's mod version so entertaining and close to a professional game that they offered to make it a stand-alone retail issue. Killing Floor was released on May 15, 2009. The original release was planned for May 14 but it was delayed 6 hours due to issues with the mainserver.

The game takes place in London, England. Horzine Biotech, a biotechnology company, is contracted to conduct experiments of a military nature involving mass cloning and genetic manipulation. Something goes horribly wrong during the process of the experimentations, and human subjects begin to exhibit grotesque mutations and disfigurement. They become increasingly hostile, and eventually overrun the internal security forces of the corporation.

Hours later, the first waves of the specimens break out onto the surface, disrupting a peace protest outside the well-known military contractor. Despite the best efforts of local police, the civilians are quickly overwhelmed and consumed by the seemingly endless supply of clones now streaming from the gaping maw of Horzine Biotech's headquarter. Having escaped their sterile prison, the creatures began to fan out to neighboring areas, devouring the helpless citizens of London while the Metropolitan Police bravely but fruitlessly attempt to stem the tide of mutated flesh now spreading across their city.

Desperate to contain the outbreak, the British government begins to organize ragtag teams of surviving British Army soldiers and Special Branch police officers to fight back against the hordes of mutated "specimens" now running amok throughout the capital and its outskirts. The player takes the role of an anonymous member of one of these teams as they partake in a variety of missions in and around the city of London.