On July 24, 1998, a series of bizarre murders occur on the outskirts of the Midwestern town of Raccoon City. The Raccoon City Police Department's Special Tactics And Rescue Service (STARS) are assigned to investigate. After contact with Bravo Team is lost, Alpha Team is sent to investigate their disappearance. Alpha Team locates Bravo Team's crashed helicopter and land at the site, where they are attacked by a pack of monstrous dogs, killing one of the team. After Alpha Team's helicopter pilot, Brad Vickers, panics and takes off alone, the remaining members (Chris Redfield, Jill Valentine, Albert Wesker and Barry Burton) seek refuge in an abandoned mansion, where they split up.
The player character (Chris or Jill) finds several members of Bravo Team, including Kenneth J. Sullivan being eaten by a zombie; Richard Aiken, who is either killed by a giant venomous snake or eaten by a shark; Forest Speyer, who is found dead and revived as a zombie; and Bravo Team leader Enrico Marini, who reveals that one of Alpha Team's members is a traitor before being killed by an unseen shooter. Bravo Team survivor Rebecca Chambers joins Chris. The player character learns that a series of illegal experiments were undertaken by a clandestine research team under the authority of a biomedical company Umbrella Corporation. The creatures roaming the mansion and its surrounding areas are the results of these experiments, which have exposed the mansion's personnel and animals to a highly contagious and mutagenic biological agent known as the T-virus.
The player character discovers a secret underground laboratory containing Umbrella's experiments. There, they find Jill or Chris in a cell and encounter Wesker programming a Tyrant, a humanoid bioweapon. Wesker reveals that he is a double agent working for Umbrella, and plans to use the Tyrant to kill the STARS members. In the ensuing confrontation, Wesker is apparently killed and the player character defeats the Tyrant. After activating the lab's self-destruct system, the player character reaches the heliport and contacts Brad for extraction. The ending changes depending on the player's actions at key points: in the best ending, the surviving team members escape by helicopter after defeating the Tyrant again; in the worst ending, the mansion remains intact and the player character is the sole survivor.
