(Capcom's primary storyline)
X-Day was Umbrella's term for the S.T.A.R.S. mission to the Arklay Mountains. Albert Wesker and Sergei Vladimir are tasked with removing the evidence of Umbrella's experiments before S.T.A.R.S.' arrival.
Wesker's orders are changed on July 24 when it became known that the S.T.A.R.S. Bravo Team survived their helicopter crash (Wesker sabotaged it). Hoping to avoid any searches for the missing members being conducted, Wesker led Alpha Team to the region himself.
Upon arrival, Wesker began searching for and destroying the incriminating evidence. When one of the surviving Bravo Team members (Enrico Marini) became wise to a traitorous presence among S.T.A.R.S., Wesker murdered him.
Upon his arrival at the Arklay Laboratory, Wesker was tasked with collecting at least two samples of each of the B.O.W.s besides the Tyrant (T-002 Type) which he was to dispose of. He anticipated this as an opportunity to leave Umbrella by way of faking his death by using a special virus engineered by William Birkin.
Wesker waited for the survivors to discover him which he injected himself with the virus and proceeded to awaken the T-002. The creature impaled Wesker with its claws before hounding the survivors.
The scheme worked and the virus saved Wesker. Upon awakening, he discovered that the self-destruct system was activated and escaped from the area (Accosted and pursued by Lisa Trevor along the way) through the mansion's front door.
Umbrella branded X-Day a failure due to the S.T.A.R.S.' survival, Wesker's supposed death and the lack of surviving samples.
The evidence existed that suggested that any person involved in the Mansion Incident was to be killed or silenced. Several attempts are also made on the lives of potential courtroom witnesses.
- Bravo Team's helicopter was sabotaged to crash.
- A page of a Will that described Wesker's appearance at the mansion was torn out.
- Enrico Marini was assassinated to prevent him from confirming the traitor's identity.
- The people's faces on the portraits on the Eastern staircase are painted out.
- Barry Burton was blackmailed by Wesker into killing the other S.T.A.R.S. members.