Resident Evil Zero

The main gameplay feature of Resident Evil Zero, dubbed the "partner zapping" system, is unique in the series in that instead of choosing a single character to play through the game, the player controls both of the main characters through the entire game: Rebecca Chambers, STARS Bravo team's medic from the original Resident Evil, and Billy Coen, an escaped ex-military convict. Both characters can travel together, with one character being controlled by the player and other by the computer, or split up and search separate areas each at the same time. This dual control is central to solving some of the puzzles in the game. The difference between the characters is that Rebecca can acquire chemicals with her mixing kit and can get into tight spaces, but has less health. In contrast, Billy can handle heavy objects, has a lighter and can sustain more damage than Rebecca, but cannot mix herbs.
The game also does away with the use of boxes placed in fixed locations for the player to store items in. Instead, the player can now drop items on the floor to make room for new ones, which they can later retrieve for future use. The locations of dropped items are displayed on the player's map.


On July 23, 1998, special police STARS Bravo Team is sent in to investigate a series of grisly murders in the Arklay Mountains region outside of Raccoon City. On the way to the scene, Bravo's helicopter malfunctions because of a sabotage and is forced to crash land in the forest. The team soon discover an overturned military police transport truck, along with the mutilated corpses of two officers. The team split up and Bravo team's field medic, Rebecca Chambers, finds a train stopped in the middle of the forest.
Rebecca soon discovers that the train, the Ecliptic Express, is infested with zombies. After a little exploration, she teams up with the man the military police were escorting to his execution; former U.S. Marine Billy Coen and the two explore the remaining train compartments while combating the zombies, swarms of strange leeches, and a mutated scorpion. As the train begins speeding out of control towards a cliff, the two manage to apply the brakes and divert its course towards an abandoned research and training center.
The pair investigate the underground facility, being forced to defeat the Umbrella Corporation's experiments: mutated insects, spiders and primates. During their navigation, Billy reveals that his unit was forced to kill the innocent civilians of an African village in the midst of a civil war against his wishes, and he soon found that their actions were based on false information. They discover that the former operator of the facility James Marcus, along with Ozwell E. Spencer and Edward Ashford, discovered the Progenitor virus which, when combined with the ebola virus, created a strain that, despite being photosensitive, caused rapid mutations. Ashford originally wanted to use the virus to help the handicapped through its regenerative effects, but after his death Spencer and Marcus began research on its applications for bio-weapons, combining it with leech DNA which eventually led to the formation of the zombiefying T-virus. After a showdown with a gigantic bat inside a church, Billy is attacked by a T-virus infected primate and becomes lost inside an underground laboratory.
While searching for him, Rebecca meets fellow Bravo Team member Enrico Marini. He tells Rebecca about 'an old mansion which Umbrella uses for research' not far from the facility. Rebecca declines Enrico's offer to follow him there, instead deciding to continue her search for Billy.
Then Rebecca fights a released Tyrant before finding Billy washed up on a walkway.
After fighting the Tyrant together, the two eventually meet Marcus. It is revealed that both Albert Wesker and William Birkin were oblivious to the cause of the outbreak in both the Ecliptic Express and the mansion, and that the real culprit was Marcus, an employee of Umbrella who operated the facility until his assassination by Wesker and Birkin, on the orders of Spencer. During his dying moments, his pet queen leech entered his body and reproduced exponentially over ten years to absorb his DNA and memories to bring him back to life. Marcus proceeds to split into a mass of leeches, before chasing Rebecca and Billy through the facility. Birkin activates the self-destruct system as the Queen Leech, Rebecca and Billy continue to fight. After being injured due to a brief exposure to sunlight, the monster is paralysed when the overhead entrance to the laboratory is opened just as the sun rises. Rebecca throws Billy a Magnum revolver and he delivers the final shot to the Queen Leech.
As the facility crumbles, the two escape into the forest and come to a halt on a cliff overlooking the Spencer estate. They salute one another after Rebecca declares Billy "officially dead". Each goes their own way, with Rebecca heading towards the mansion to investigate the whereabouts of Bravo team. Immediately after the mansion would detonate or not. (depending on the different endings of Episode 1)