RESIDENT EVIL ZERO | Part #1 Gameplay Walkthrough

On July 23, 1998, a train owned by the pharmaceutical company Umbrella, the Ecliptic Express, comes under attack from a swarm of leeches. As the passengers and crew are attacked, a mysterious young man watches from a hillside. Two hours later, the Bravo Team of the Special Tactics And Rescue Service (STARS) police force is sent to investigate a series of cannibalistic murders in the Arklay Mountains outside of Raccoon City. On the way to the scene, its helicopter has an engine failure and crash-lands in a forest. Searching the area, officer Rebecca Chambers of Bravo Team comes across the Express, now motionless. She begins to investigate the scene, only to find the passengers and crew transformed into zombies. She is unaware their transformation is a result of exposure to Umbrella's T-virus contained within the leeches. As she explores the train, she teams up with Billy Coen—a former Marine Force Reconnaissance officer, who was to be executed for killing 23 people until the military police van transporting him crashed in the region.

The pair notices the mysterious young man, moments before the train suddenly begins moving again. Unbeknownst to the pair, two soldiers from Umbrella, on the orders of Albert Wesker and William Birkin, attempt to take control of the train and destroy it, but are killed by leeches before they can complete their mission. As the train speeds out of control, Rebecca and Billy apply the brakes and avert its course towards an abandoned training facility for future executives of Umbrella. They discover that the former director of the facility and the corporation's co-founder, Dr. James Marcus, was responsible for discovering the so-called Progenitor virus in the 1960s, and decided to examine its potential as a biological weapon. He combined it with leech DNA to develop the T-virus that causes rapid mutations in living organisms and thus transforms humans and animals into zombies and monsters.

As the pair continue to explore the facility, Wesker decides to leave Umbrella and join its rival company, and makes plans for further research on the T-virus. William Birkin refuses his offer to join him, instead opting to complete his research on the G-virus. Later, Rebecca becomes separated from Billy. On her own, she encounters Captain Enrico Marini, who tells her that the rest of the Bravo team will meet up at an old mansion they found, but allows her to stay behind to find Billy. Just after Enrico leaves, Rebecca is attacked by the Tyrant. After temporarily defeating the Tyrant, Rebecca meets up with Billy again and, together, they defeat it and continue on towards a water plant.

Eventually, Rebecca and Billy catch up with the leech-controlling man, who happens to be Marcus' final experiment, Queen Leech. In 1988, Marcus was assassinated on the orders of Umbrella's other co-founder, Oswell E. Spencer, who sought his research. After his corpse was dumped, Queen Leech entered his body and reanimated it, gaining his memories and the ability to shapeshift, thus believing itself to be the resurrected Marcus and orchestrated the T-virus outbreak in the facility and on the train as a means of revenge against Umbrella. After temporarily defeating it, Billy and Rebecca attempt to escape to the surface via a lift, just as William Birkin trips the facility's self-destruct mechanism. Pursued by Queen Leech, the pair eventually kill it and escape before the facility is destroyed. Following their escape, Rebecca notices the mansion that Marini mentioned and prepares to head for it. Before she does, she assures Billy that her police report will list him as another casualty of the incident. Thanking her for his freedom, Billy departs as Rebecca heads towards the mansion to seek out the whereabouts of her fellow Bravo Team members (seen in Resident Evil).