All upgrades add money.
History is such a fragile thing. So very easily changed with the most insignificant event... or by the most significant one. 1700s Boston is about to have it's history changed forever, and it's up to George Washington (you) to stop this from happening.
It all started in the future, when a bunch of aliens thought it would be fun to send zombies into the past to mess up human history. After careful consideration, they opted to send them to 18th century America. Chaos is about to begin in the past, so before it gets out of hand, back in the present, the FBI combined with some funky magical order have devised a time traveling machine and a genetic clone of George Washington. They mean to send both back to the past to undo the damage caused by the alien zombie horde.