Apparently Riordan wanted a switch from Greek. He got it. It's not just that the names and stories have changed. All religions have an edge where they shade into magic. The Greeks and Romans disapproved of it, treating it as impiety; the biggest known witch hunts, with thousands of victims, were in the Roman Republic. The Egyptians saw nothing wrong with it. Papyrus are chock-full of passages that mix religion and magic in full doses, simultaneously imploring and threatening the gods.
So, in this book, we have Sadie and Carter Kane. Carter lives with their father, continually on the move for his job; Sadie stays with their grandparents since their mother died, and gets to see them twice a year. This year, their father decides to take them to the museum for that day. And he does something -- obviously magical -- with the Rosetta Stone, which is shattered, and lets loose something not good, and disappears.
Sadie and Carter are taken off by Amos, who has not contacted them for a long time, and who is definitely a magician. They learn of the House of Life, who do not, of course, worship the gods; they use them in magic, or did. They meet a baboon and an albino crocodile and learn of portals, and obelisks, and how to trap a god. Of Sadie's kitten Muffin. And just what their parents had been up to when their mother died, and why.
It's a first person account, but unlike Percy Jackson, it switches between them. And they are dictating it to a recording for a purpose that becomes clear at the end, and with comments about what they are doing and what the other sibling thinks of what they are saying. A somewhat different effect.