Billy Coen. If they travel together, either one of them can be controlled while the other character is handled by the game's artificial intelligence (AI). The player may also control both simultaneously or split them up to explore areas separately. Each character has unique abilities. Rebecca has a mixing kit which allows her to combine herbs and other chemicals, but she is weak defensively. In contrast, Billy can move heavy objects, use a lighter, and has higher defense, but cannot mix herbs (a staple ability in Resident Evil games). The partner system is central to solving many of the game's puzzles. The characters can run as well as perform quick 180-degree turns to evade danger. The player may examine objects such as doors, other characters, and items in order to find clues to proceed through the game. Some objects can be pushed or climbed upon to investigate higher levels. Items held by the characters can be examined in the inventory screen. Some items such as weapons can be equipped, and other items can be combined to create more effective items or replenish ammunition. When Rebecca and Billy are close by, they can exchange items between one-another. Previous series installments had the player store items in boxes placed in fixed locations. Resident Evil Zero has no item boxes, and instead allows players to drop items on the floor, freeing space in the inventory momentarily until they are retrieved at a later point. The locations of dropped items are displayed on the game map. The number of items that can be discarded in a room is limited. A bonus game, Leech Hunter, has Billy and Rebecca each collect leech charms in the mansion. Plot 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