Setting
The underwater city of Rapture
The game takes place in 1960 in a fictional large underwater metropolis called Rapture, built on the seabed in the mid-Atlantic Ocean. Built in 1946 by Andrew Ryan, Rapture is designed to be entirely self-supporting, with all of its electricity, food production, water purification and defense systems powered by undersea volcanic openings. During the early 1950s, Rapture's population peaked at several thousand, and was composed of people Ryan viewed as the best examples of mankind. A large and tiered economy grows among the people, catering different quality products to different levels of the society.
A scientific discovery upsets the balance of the society. A young German scientist named Bridgette Tenenbaum discovers a species of sea slug that could secrete pure stem cells. These could be used to enhance one's body, improving physical or mental capabilities, curing diseases and healing injuries. Needing a financial backer and supplies for her research, and having been turned down by all the respectable labs, she turns to Frank Fontaine, the leader of a smuggling ring inside Port Neptune.
Plot
The game opens in 1960. The player assumes the role of Jack, a passenger on an aircraft that crashes into the middle of the Atlantic Ocean. Jack swims for the only structure he sees, a lighthouse that serves as the above-surface entry point into Rapture - a grand metropolis under the water. Descending into the city using a bathysphere, he learns of the original prosperous history of Rapture through a pre-recorded film, narrated by the founder of Rapture, Andrew Ryan, but, upon arrival, Jack discovers that the once-prosperous city has decayed into a shadow of its former self. He is quickly led to safety by a man named Atlas, who communicates to Jack over a short-wave radio; Atlas believes that Jack is his only hope in reuniting with his wife and child. After moving through several levels of flooding infrastructure, the player is discovered by Andrew Ryan, who communicates with the player, assuming him to be an intelligence officer sent by either the KGB or the CIA.
Enemies
Four main categories of enemies are encountered:
* Aggressors (Splicers): Deformed, genetically modified Rapture citizens who are now remnants of Ryan's army, the Aggressors cannot survive without ADAM due to their extensive biological modifications. Early Splicers seem to be referred to according to their weapon preference, such as "Leadhead" for those who prefer guns. They wear little or no armor, and normally roam the levels of Rapture, searching for other inhabitants to kill and steal ADAM from. As their name would suggest, they are aggressive and quick to attack, and will use their enhanced physical strength, group tactics and, sometimes, semi-biological weapons to kill all in their path. Most of the Splicers are wearing the masquerade ball masks that were worn during the 1959 New Year's Eve party. (One character muses, "I wonder why they wear the masks? Maybe it's because they have a shred of humanity left, and they're ashamed of what they've become.")
* Gatherers (Little Sisters): The Little Sisters are genetically modified prepubescent girls. The Gatherers, whom Dr. Tenenbaum created as a solution to the ADAM shortage, extract the inert ADAM from the dead (which they call "angels") using retractable needle syringes and then consume it, their bodies reprocessing it into a usable form. The BioShock team designed these characters in order to draw out an emotional response from players, who face an ethical choice between saving or murdering little girls to obtain a much-needed resource. Nevertheless, doing so is severely difficult due to their symbiotic relationship with the Protectors. According to lead designer Ken Levine, the Gatherers have a direct link with the main character. In a recently released audio file, Levine clarifies that the player cannot physically harm a Little Sister directly, but can "harvest" the ADAM from them (a process which they will not survive), by forcibly extracting the sea slug from within their bodies. This will be presented via audio, and a black screen.[14] Players are also given the option to "rescue" the Gatherers, which nets only half the ADAM of a harvest, but makes an ally of their benefactor, Dr. Tenenbaum, who presents herself early in the game, providing the tools needed to rescue these creatures, along with promises of future compensation. This compensation, among them plasmid upgrades few other inhabitants of Rapture possess, makes rescue a desirable long-term strategy. Ultimately, the player's decision vis-à-vis the Little Sisters will influence the game's ending.
* Protectors (Big Daddies, or Mr. Bubbles and Mr. B as the Gatherers call them, also called Metal Daddies by Splicers): Mute, lumbering bio-mechanical monstrosities, created to protect the Gatherers. They are heavily armored and wield high-powered weaponry, usually including a large drill. Their armor somewhat resembles a large diving suit. Most of the inhabitants stay out of the way of the Gatherers and Protectors. They will not attack the player unless provoked and according to lead designer Paul Hellquist: "Once you mess with them, you find out why no one messes with them." In a recent trailer/commentary for BioShock, it was revealed that, despite their size and typically slow movements, they become incredibly fast once engaged, in some cases quicker than the player character. However, the player can defeat them easily enough if the correct plasmids are used, such as shooting bolts of lightning at a Big Daddy standing in a pool of water. There are two types of Big Daddies: Rosies and Bouncers; Bouncers are the close combat type with different detachable arm-mounted weapons, one of which is a drill. Rosies attack from long range due to the large rivet gun they are armed with. A Big Daddy that has no associated Little Sister to defend will plod about and look in decorative art-deco holes in the wall where Little Sisters are known to hide. If the player gets in their way while they search, then the Big Daddy will casually swat the player aside without a second glance and continue investigating.
* Security Bots: Throughout the city of Rapture, they are called via alarm by various security cameras. Security bots hover and fly using rotors and are armed with machine guns. When disturbed, the security cameras' siren will sound and an unlimited supply of security bots will pour out for a limited time. There are three ways of taking down security bots: the player can attempt to destroy them, shut off the security system by paying the money demanded to access a Bot Shutdown switch, or manually hack into their systems. Hacking bots and other mechanical devices prompts a mini-game resembling Pipe Dream. The security system can also be suborned by the player, either by "hacking" it or using the "Security Bullseye" plasmid on an enemy.
Main characters
* Jack
* Andrew Ryan
* Bridgette Tenenbaum
* Atlas
* Frank Fontaine
Minor characters
* Dr. J.S. Steinman
* Dr. Suchong
* Bill McDonagh
* Diane McClintock
* Sullivan
* Peach Wilkins
* Professor Julie Langford
* Sander Cohen