Athenide AU, but Lester is thrown back in time (maybe from a separate timeline?) too.
During Nero and the emperor's bullshit (still haven't read the books, working on it) Lester is somehow trapped back in Ancient Greek days, as Lester. Lester is freaking out and has to get back to modern times and the only person he can think to go to for help is his wife, Perse.
Only she isn't his wife yet. Perse and Apollo are close, but Lester still isn't entirely sure when Perse fell in love with him but he's desperate to see her again. Even if Leto or Artemis were an option, would either recognize him? Would they think him an imposter? At least Perse never smote someone.
Perse, obviously, is still Percy and still has her memories of Percy, so all Lester has to do is explain what the modern day is like for her to realize, "Oh, this Lester is from around Percy's time". But she doesn't really know how to get him back too--she's been trying to find her own way back--and Lester is very delicate and alone and cute, so she keeps him with her in her temples.
Anyway, that's how the Olympians discover the Athenide's first and only mortal lover, some guy named Lester.
















