New York City, 1929: welcome to the height of the American Prohibition. The Five Families have cornered the illegal liquor distribution in all five boroughs of the city. Your father, the Don of the Leonesi Family Mafia, is assassinated on the street: inheriting the crown, it is now up to you - as boss - to restore the supremacy of your Family and take back the streets that you used to own. Capo di tutti capi.
The city is corrupt from the inside out, however. The Politicians run the show, and you're going to have to keep them on-side if you want to succeed. Liquor distribution may be illegal, but nobody is gonna stop you if they're taking a cut of your profits. Bribery is only part of the game, but money goes far - and allocating it is a skill.
Start shooting up the streets, however, and you'll soon find yourself involved with a lot of unnecessary attention from all sides - especially the City Police - so you're going to have to be subtle with violence, if you want to make money.
Similarly, keeping your public satisfied is crucial because they're your main source of income. If you want to maintain those huge alcohol profits, you need to look after your community: violence on the streets will reduce the people's respect for your Family, making you less money in the long-term.
Keeping your districts stocked up with alcohol, to meet demand, is the most important thing of all - your liquor crates are ordered and shipped into the city Sea Ports at night by boatload, which means keeping a level of respect with the Dockers Unions that run operations on them. It's a thirsty town.
Your Family, the Leonesi Mafia, run Staten Island - the least-prestigious and smallest borough in New York City. Building up your districts, shipping crates of liquor, upgrading the quality of your alcohol, arming your mobsters on the street, maintaining your city connections, and going to war with the four rival Mafia Families are all part of your journey towards owning the entire city and achieving the title of Boss of all Bosses.