Mansion Incident

The Mansion Incident was the first stage in a series of events that led to the destruction of Raccoon City in the Sterilization Operation. The epicenter of this incident was in the north-west Arklay Mountains, eight miles into the Raccoon Forest.

Events
On May 11, Dr. James Marcus, who had been resurrected by the Progenitor virus via a leech colony that Marcus had experimented on, enacted his vengeance on Umbrella for his assassination ten years prior. His vengeance was enacted by the spreading the experimental t-Virus around the Arklay Laboratory. While the laboratory staff protected themselves in Hazmat suits, it became evident soon after that, it was already too late.

The infirmary began treating staff members with swollen skin around the 13th, though they were only able to put bandages on the wounds of the animal keeper, whose skin began to display decomposition over the next few days.

It was on May 14 that the Cerberus pack broke out of their cages, escaping into the mountains. Meanwhile, the laboratory executives became aware of the viral outbreak and promptly sealed-off the facility - a man trying to escape was consequently shot.

On May 21 the animal keeper's sanity degraded so much that he murdered and then consumed his friend, Scott. Martin Crackhorn committed suicide on June 3 in the hopes that he would escape the fate of his now-undead colleagues.

S.T.A.R.S. investigation
Afterwards, from June to July, more reports of unusual deaths and mysterious wildlife sighted at the Arklay mountains were cited. Because of these reports, the roads to the Arklay Mountains were closed off by the police on July 9 and the S.T.A.R.S. Bravo Team, led by Enrico Marini, were dispatched to investigate.

Unbeknownst to either Umbrella or S.T.A.R.S., the viral outbreak in the Arklay region was deliberately engineered by James Marcus. Umbrella later sent a fax to their agent and head of security, S.T.A.R.S. Alpha Team Captain Albert Wesker, into luring the S.T.A.R.S. Team into being killed by the now-rogue B.O.W's. On July 23, the S.T.A.R.S. Bravo Team's helicopter was forced to crash land due to an engine failure.

Around the same time, the Ecliptic Express train also become infected with the t-Virus via Marcus' leeches, screeching to a halt, to which Rebecca Chambers, a member of Bravo Team, discovers. Likewise, Bravo Team's primary pilot, Kevin Dooley, was killed by the escaped Cerberus pack, whereas the co-pilot, Edward Dewey, managed to survive the attack, but soon succumbed to his wounds upon entering the Eclipse Express, though not before warning Rebecca that there were zombies and monsters in the forest.

Wesker, alongside researcher William Birkin, observed the events, and also gave commands to the Umbrella investigative squad on the train until they met their own ends at the hands of Marcus' leeches and were promptly infected.

Bravo Team eventually managed to arrive at the Spencer Mansion, while Chambers arriving at the Umbrella Research Center with an escaped convict, Billy Coen. Wesker and Birkin were also surprised by Marcus' apparent revival, with Wesker departing to take care of the escaped prototype tyrant, leaving Birkin to activate a Gondola.

The next day, these events also forced them to activate the training facility's self-destruct protocol, to which Wesker also decided to leave Umbrella. Wesker also had to contend with an Ivan dispatched by Sergei for his disobedience, although the self-destruct devices activating allowed Wesker an opportunity to escape when Sergei and the Ivan were forced to block the explosions, also retrieving the T-A.L.O.S., an event which Rebecca and Richards briefly witnessed before being attacked by the Yawn B.O.W.

Likewise, Wesker himself led Alpha Team to search for the missing members of Bravo Team, and were then forced to hide out at the Arklay Mansion after the discovery of the Bravo Team's crashed helicopter ended in an ambush by Zombie Dogs that resulted in the death of Joseph Frost. Wesker then had Barry Burton lure the rest of his team into various traps, under the threat that Wesker kill his family if he doesn't do so.

Alpha Team members Chris Redfield and Jill Valentine later discover Enrico Marini in the caverns of the mansion, and reveals that he found some evidence of a traitor within the unit, citing that he managed to draw it down to two suspects, Wesker and Redfield. However, he is then gunned down by an unknown assailant (actually Wesker) and killed, although not before he hints that Umbrella was responsible for the disaster in his dying breaths.

Wesker then planned to steal the Tyrant for himself, also injecting himself with a prototype virus, having anticipated the possibility that the Tyrant would murder him when he released it. They later find the laboratory and find Wesker among the photos, causing them to learn that Wesker was in fact the traitor to the unit. Wesker then attempts to sic the Tyrant on them, but as he had anticipated, the Tyrant turned against him and impaled him before going after them.

Jill and Chris later wound the Tyrant and seemingly killed it, although it was revived shortly thereafter. Likewise, the prototype virus also allowed Wesker to survive the Tyrant's earlier attack, also imbuing him with superhuman abilities at the cost of his humanity.

Jill, Chris, and Rebecca all escape after killing the Tyrant once and for all, as well as set the self-destruct device, with Barry Burton also aiding in the escape effort. Wesker, meanwhile, also escaped, and had ran a mile away from the mansion before the self-destruct device went off, also killing Lisa for good in the process. Afterwards, S.T.A.R.S. was disbanded after they supplied their report on the events on the Arklay incident, mostly due to Brian Irons' being paid off by Umbrella to cover up the incident.