The annihilation of Raccoon City shocked the entire nation. This devastating incident began with a virus-leaking accident in a single mansion. That immense mansion, built deep in the forests of the Arklay mountain range, was built by the architect George Trevor, who was commissioned by Ozwell E. Spencer. However, this man was in fact the Arklay Research Facility, where Umbrella was conducting experiments for biological warfare, culminating with the T-Virus. The unpredictable biological accident was to envelop all of Raccoon City in an inescapable nightmare.

In June 1998, a local weekly newspaper received reports of Cerberus sightings. In July, victims continued to be discovered in the Arklay Mountains. The Raccoon Police Department immediately sealed off the mountain roads and due to strong public demand, ordered S.T.A.R.S. to begin an investigation of the area. Bravo Team, led by Captain Enrico Marini, was deployed. Soon after, they were declared missing in Raccoon Forest and headquarters ordered Alpha Team to search for their missing comrades.

It was then that Alpha Team encountered the pack of Cerberuses that had escaped from the Arklay Research Facility. In avoiding the Cerberus attack, a number of Alpha Team members fled to the Arklay Research Facility. However, due to a series of devices and betrayals, they were scattered and faced peril at every turn within the zombie-infested research facility. These events were passed on and dubbed the Mansion Incident. Only 5 members of S.T.A.R.S. survived the unprecedented and tragic occurrences. However, their report was for naught. All of Raccoon City was paralyzed by the tremendous biological disaster and the citizens received the nation's sympathy.