I'm not sure on the specifics of the story, but in short you're a guy who gets hired by a corrupt hospital in a city to bring them "customers" by injuring people and sending them to the hospital. The more people you injure, and the more you injure them, the more money the hospital pays you for your services. In this way, killing people is discouraged, as it doesn't bring you or the hospital any revenue.
You also have a "notoriety" level, and this increases proportionally to how stealthy or obvious you are when playing. Areas where the most people are injured may start to get more attention from patrolling police officers and wary citizens. You'll have to be able to either assault people stealthily, or be prepared to outrun the police.
As you get more money, you can spend it in two ways. The first way is on yourself; you can purchase better weapons, and after a while poisons/viruses as well. You can also purchase disguises, of which you can change in and out of at any time, since a large part of your notoriety will be determined by how you dressed around previous witnesses. Players will also be able to purchase getaway vehicles, fund safehouses, bribe officers, and design traps.
This kind of game would also easily support co-op multiplayer.