SiN is a first-person shooter video game based on a modified version of the Quake II engine developed by Ritual Entertainment and published by Activision in late 1998. The game was later released over Valve Software's Steam Platform on April 5, 2006, either as a standalone product, or bundled together with its sequel, SiN Episodes.
Set in the near future of 2037, many of the levels and locations are reminiscent of their current day equivalents. Banks, building sites, sewage works and other everyday recognizable buildings form the basis of many of the levels in SiN. One major difference in the world of SiN is the lack of a police force. Ten years prior to the game, the police force collapsed due to corruption and ineffectiveness against the rising tide of crime. Private security companies have taken the police's place, with some of them patrolling the streets like the former police, some in charge of protecting their employer's assets.
One of these companies which employ their own armed security forces are SinTek, a large multi-national biotechnology corporation specializing in medical and chemical research, owned by the beautiful and charismatic Elexis Sinclaire. Elexis took over the company following the mysterious disappearance of her father, Dr. Thrall Sinclaire, who founded it in 2005.
The protagonist of the game, colonel John R. Blade, is the commander of one of the largest security forces in the city of Freeport, HardCorps. Prior to the beginning of the game, Blade is working to rid the streets of a potent new recreational drug named U4, which is rapidly gaining popularity in Freeport and is rumored to be able to cause genetic mutations to its users. Yet, the source of the drug is still unknown, and its effects not entirely studied. As the game begins, the player is placed into the shoes of John Blade as he responds to a full scale bank heist and hostage situation perpetrated by a well known Freeport criminal boss, Antonio Mancini. But as the player progresses and pursues the criminal behind the heist, further questions are raised: Who is really behind the heist? And is this linked to the reported appearances of mutants in the city?
As the game progresses, it is gradually revealed that the whole bank robbery is funded by Elexis Sinclaire, who in fact only wanted Mancini to steal a safety deposit box from the bank's vault. When she learns that he launched a full-scale bank heist instead, she injects him with concentrated U4 and turns him into a mutant, sending him after Blade. John manages to defeat the huge creature, and afterwards learns that it was in fact Mancini himself. Blade also finds out that the substance found in Mancini's body after his death, is only manufactured by one company - SinTEK. All these unavoidable facts force Blade to embark onto an investigation into SinTEK's vast industrial area located in the outskirts of Freeport.
Later, Blade learns that Elexis Sinclaire's main goal is to poison the Freeport water system with vast quantities of U4, turning all of the city's inhabitants into mutants. He manages to thwart that plan, but it turns out to be just a diversion, because in the meantime, SinTek's troops steal nuclear warheads from a U.S. military base. Elexis threatens to fill them with U4 and launch them at specific targets, turning the entire world's population into mutants. As Blade becomes aware of that, he heads to SinTEK's main base in order to stop Sinclaire.
Throughout the missions, Blade is aided via radio link by a computer expert working at HardCorps: JC, a skilled hacker, capable of breaking into even the tightest of networks. In fact, Blade had first found out about JC when investigating a cracker who had broken into the HardCorps system. After tracking down the hacker, Blade, recognizing the perpetrator's talents, decided to make him a job offer at HardCorps instead of arresting him. Thus, JC became one of HardCorps most valuable assets and the only one able to assist them in hacking-based missions.