Re: Percy Jackson and the Olympians
the premise is that the Greek mythos is alive and well in the current world. As Western civilization has moved west, so has the gods. Currently, Mount Olympus is above the Empire State Building.
The main characters are all half-blood children of the gods. Percy Jackson is the son of Posiedon, the only currently surviving decendent of one of the big three (Zeus, Posiedon, Hades). The big three made a pact after WW II not to breed with humans, as those children tend to cause a great deal of mischief. That pact has been broken twice since then, once by Zeus and once by Posiedon.
The world is full of monsters, but because of a magical mist, mundanes do not realize it. Instead, they see something that is easier for the minds to accept.
Each novel, Percy is assigned a quest. In the first, he has to travel to Hades to recover Zeus' most prized lighnting javelin, which Zeus believes Percy has stolen and is about to go to war with Posiedon over. Percy travels there with his friends, Grady the Saytr and Annabelle, a daughter of Ares.