Not Your Savior

Sequel of The Demons in Disguise by PercyFanHOo
It's been a year, and the former heroes of Olympus finds strange guests at the door, taking their children and themselves. The heroes are loaded into a van and taken to a desecrated, destroyed campsite.
Who is the small mercenary? And most importantly, who is 'The Demigod'?
(Note, I don't own any of the characters, they belong to their creators)