At its heart, SINS is a narrative role-playing game, specifically focused on telling the stories of powerful entities known as Nemissaries, reborn individuals back from the dead with a wealth of mysterious powers, who have risen once more to fight an eldritch hive-mind of the undying, known as the Brood, in the post-apocalyptic ruins of a 22nd Century Earth.
Sins takes place in our own world, albeit about a century from now. The world as we know it is gone, replaced with a bleak post-apocalyptic wilderness.
Some areas of the world have been scorched by nuclear weapons, and others have returned to their natural state, but the one constant is that mankind is no longer the master of the world.
Large nations or civilisations are rare, and most contact takes place primarily on a local level between nomadic groups and small settlements.
There are exceptions however, and one of the core themes of the game is the re-emergence of civilisations.