As a rule, I try not to be over-specific when it comes to prompts; elsewise, I might as well write my own story. (Which I can't do for this crossover at present, as I haven't near enough PJO knowledge to even begin.)

This one clearly could have gone in a much zanier direction, and while I'm definitely onboard with high levels of inspired zaniness, I'm just as glad it didn't. And while this is reasonably self-contained, I think you're right that it's also a potential springboard for further developments. (One has to wonder how this revelation is going to affect Beckett's relationships with the various Castles, for instance....)