The immortal fire

"After their near-fatal battle with Poseidon, Charlotte and Zee would love nothing more than to relax and forget that the Greek gods are real. But with the world in peril and no one else to save it, that just isn't an option. Charlotte and Zee are approached by the Prometheans, an ancient brotherhood who protect mankind from the whims of the gods. They think they've finally found a weapon capable of bringing Zeus to his knees. But using it would come at a great cost, one Charlotte and Zee are not willing to pay. Deciding that, this time, the gods are the lesser evil, the two strike out for Mount Olympus with the Prometheans, an angry Chimera, and other mythological beasts following close behind"--