Essentially when great heroes from any place in the world die, they go to a spaceship called the Santa Maria. It contains a number of heroes from America's past, such as George Washington, Theodore Roosevelt, and Nikola Tesla. These people serve as friendly NPCS for the player, with Washington as the leader of the ship, dolling out missions and serving as a leader for all of the other heroes. Roosevelt is the drill sergeant, instructing new recruits about how the world functions and offering to train them. Tesla is the Q of the world, creating new equipment and acting insane.
Basically the ship travels through space because everyone on board believes that it can, and the belief is what carries it to the right places. When arriving on a new planet or opposing ship a raiding party is sent out, generally consisting of the party, and often one notable historical figure, and they go in and defeat the forces of evil. These include vague threats like evil, or unhappiness, represented by physical things like demons or an enormous cloud of darkness, but others are are forces like a stereotyped Redcoat, British oppressors.