From the introduction:
Welcome to the world of Percy Jackson and the Olympians! In this world the myths of ancient civilization were and continue to be quite real, still existing today as modern culture and belief sustain their existence. It is a world of monsters and adventure, one kept up thanks to the mystical force known as “The Mist” which hides supernatural events from mundane eyes. Children of the Gods, known as Demigods, often go on quests that decide the fate of the world as we know it, while ultra-powerful beings seem to plot to destroy it every second. Yet somehow, everyone manages to get a decent education and have a good time when nothing too major is going on. Perhaps it isn’t as bad as it looks?
You’ll begin on the Month of June, a few weeks before the events of the Lightning Thief starts.