I got it today...if I haven't mentioned it anywhere else...I get distracted and sometimes forget if I posted things already.
But I LOVED The Red Pyramid. And it pleased me that the myth of the 'demon days' was an original story--not just by Riordan. I read about, found a different version than his, in fact, tweaked it A LOT, and added it to my last novel. It was amazing.
That's what I do: I read the old myths (mainly Greek and Egyptian) and tweak them so much that they are almost entirely new myths. I wrote a whole novel (my second one, in fact) around an elemental sword of six elements (Wind, Water, Fire, Earth, Spirit, and Time) created by the Greek gods. And that sword ended up being in the latest novel and its prequel; two different series, but still tied together.
Side note: I thought The Lost Hero was great! I can't wait for the Son of Neptune.