What are a couple main events that led to Percy's finding the stolen lighting bolt in Percy Jackson and the Olympians: The Lightning Thief?

A few things happen that lead Percy to finding and
returning the stolen lightning bolt.  When Percy leaves Half-Blood Hill, the training
camp for heroes, his quest is to find and return Zeus's master bolt. Setting out on the
quest is important, but Percy does not end up finding the bolt immediately. Everyone
thinks that Hades has stolen the master bolt, so Percy journeys to the land of the dead.
Along the way, Percy meets Ares, who gives him a backpack. When Percy finally reaches
the Underworld and meets Hades, it is revealed that the bolt was hidden inside the
backpack all along.  Percy manages to escape the Underworld, battle Ares, and then
return the master bolt to Zeus.