Crazy = Genius

Percy and Sophie Foster were childhood friends. Sophie is terrified when Percy disappears during Christmas break but is whisked away in October before he comes back. This means that unlike every other person who knew Sophie, Percy never got his memory wiped.

The last thing Percy wanted to deal with after the deaths in the Giant War was for everyone he knew to start acting like one of his best friends; Sophie Foster, the girl he thought of as a sister, didn't exist. So when he's on a vacation with Paul in Texas (something about needing to get away from New York after the accident), the last person he expects to get a call from is Sophie, who tells him that her and another kid are running away from cloaked men who kidnapped them.

of course nothing ever goes to plan, and now the Lost Cities have to deal with Perseus Jackson and his step-father Paul Blofis. Oh yeah, and humans are really fucking weird.