The original game opens on the evening of July 24, 1998 in the fictional Midwestern town of Raccoon City where a number of grisly murders had taken place on the outskirts of town. Victims were attacked in their homes by a group of assailants with evidence of cannibalism. Baffled by the strange nature of the cases, the Raccoon City Police Department sent in the S.T.A.R.S. Bravo team. Their mission was to investigate a mysterious mansion out in the woods... A mission they would not return from.
After contact was lost with their compatriots, S.T.A.R.S. Alpha team quickly mobilized to find out what happened. Alpha team located the downed Bravo team helicopter, but only one body was found - the pilot Kevin Dooley, dead in the helicopter. The other six members were no where to be found... Alpha team quickly spread out to look for clues. As the group fanned out, Joseph Frost located a severed hand clutching a pistol. Frost was quickly beset by a pack of Cerberus and fatally mauled. Alpha team pilot Brad Vickers panicked and flew off, stranding the remaining four members: Captain Wesker, Barry Burton, Chris Redfield and Jill Valentine.
With no other options, the group took refuge inside what they believed to be an abandoned mansion (during the run, Chris Redfield loses his handgun. Players don't begin with it when they play as Chris). Though they find out later in the game that this mansion is in reality the Arklay Laboratory disguised as a mansion and owned by the Spencer Family. Depending on which character the player chooses, one of the four survivors will get separated from the others - Barry if playing as Chris, and Chris if playing as Jill. It is at this point that the player takes control of either Chris or Jill to explore the mansion.
Regardless of who is chosen, the first major discovery is the dead body of Bravo team member Kenneth J. Sullivan, having been eaten alive by a zombie. Another member, Forest Speyer is found - having been wounded and eventually pecked to death by crows. (Speyer will reanimate in the Director's Cut and the REmake.) The mansion is overrun with vicious monsters - ranging from zombies and zombie dogs, to giant spiders and even hostile plant-like creatures. Scattered documents and computer discs suggest that a series of experiments have been executed on the property by the Umbrella Corporation. The monsters are the results of these experiments, which have exposed humans and various animals to a specially engineered biological agent known as the t-virus (hence the Japanese title "Biohazard").
Throughout the game, Jill is aided by the veteran Barry Burton, while Chris works with Bravo team rookie Rebecca Chambers. The house abounds with strange and deadly puzzles and traps that must be overcome to advance. After navigating a series of tunnels, passageways, and other buildings on the property, Chris/Jill discover a secret underground laboratory containing detailed records of the Umbrella Corporation's experiments.
The ending sequence varies depending on choices made by the player as he/she explored the mansion. So long as the player escaped with two teammates, the ending plays out as described above. Rescuing only one or none of your teammates changes the outcome, in particular the fate of the laboratory and the Tyrant.
