You, Percy, Annabeth, and Grover were at a casino looking for Hermes. Percy, you, and Annabeth went off as a trio and Grover went on his own. There was lotus in the air that made people forget. By the time you all found Grover, he forgot who you all are.

Grover: ” Ooo, we’re on a quest? Sounds fun! “

Percy, Annabeth, and you all looked at Grover. The only way to get his memory back, was to leave.