The Red Pyramid (Kane Chronicles #1), by Rick Riordan
If the book is a middle grade novel updating mythology to the modern day, the characters are well-drawn and believable, and the subject is approached with just the right combination of humor and suspense, then it must be by Rick Riordan. Riordan made his first foray away from Greek mythology, into Egyptian mythology, in this book, which is the first book in his "Kane Chronicles" trilogy.
"The Kane Chronicles" is the story of Carter and Sadie Kane, children of Egyptologist Julius Kane. The death of Carter and Sadie's mother, Ruby, six years previously led to the breakup of their family. Carter has lived with Julius, traveling the world and being home-schooled. Meanwhile, Sadie has lived with their maternal grandparents in a London flat and going to a traditional school.
The Kane family reunites for one day per year on Christmas. The Christmas that Carter is fourteen and Sadie is twelve, they go to the British Museum. Julius ends up entombed in a magical sarcophagus, sinking through the floor of the museum and disappearing. From this moment on, Carter's and Sadie's lives are changed irreversibly.
Their uncle Amos comes to take them to his home and Carter and Sadie discover that they are the descendants of two pharaohs, Narmer (on their father's side) and Ramesses (on their mother's side). This heritage means that they are born magic-users and that they can host Egyptian gods.
Hosting is Riordan's explanation for the shifting relationships among the gods. Most Egyptian gods cannot leave the Duat, their magical realm and enter the physical world without a physical host -- a body in our world in which they can live. Descendants of the pharaohs make the best hosts, as a rule, and some who are not descended from the pharaohs cannot host gods at all.
The changes among sibling/parent, spousal, and other relationships among the gods is explained as actually being the relationships among the hosts -- Osiris had a host who was the sibling of Isis, for example. And then Osiris's host was Isis's husband. These relationships then become part of the gods' own identities.
In the "Kane Chronicles" universe, the five gods Horus, Isis, Nephthys, Osiris, and Set were the children of the sky, Nut, and the earth, Geb. In all both realities, Ra forbade Nut to give birth to her children on any of the days of the year. Nut created five more days by gambling with the moon, Khonsu, for time. She then gave birth to one child on each of these final five days. This is why the year has 365 days, rather than an even 360.
This series is a departure from "Percy Jackson and the Olympians" in an important way besides just the change in mythology. Where Percy and the other Half-Bloods are, for the most part, part of the establishment, Carter and Sadie and the rest of the Kanes are rebels. The guiding organization for the Egyptian magicians of the world is Per Ankh -- the House of Life. Over a thousand years ago, the House decided that the fall of Egypt was due to their relationships with the gods. So, they locked the Egyptian gods away and developed a magical system that excluded them. Sadie and Carter's parents found out that something disastrous was going to happen and that humanity would need the gods, so they set out to release them, which led to the death of Ruby.
This attempt to reconnect with the gods has made the Kanes outlaws, so not only do they have to achieve their quest, they have to do it while trying to evade the acting head of the House of Life -- the Chief Lector -- and his followers.
During the act of magic that caused Julius to be locked in the sarcophagus, Julius released Horus, Isis, Nephthys, Osiris, and Set. Immediately after being released, Set headed for the Sonoran desert and set up a power base, including the titular red pyramid, there under Camelback Mountain.
Carter and Sadie have to collect the things they need to defeat Set and make it to Camelback Mountain before Set's birthday, which, as the book opens, is only three days away.
As always, there is a travelogue integrated into the book. We visit Brooklyn, which is the Kane family's home base, briefly visit Central Park on Manhattan (the visit has to be brief because this is in the same universe as "Percy Jackson and the Olympians" and the two pantheons stay out of each other's way), then go to the Cairo Airport; Paris; Washington, DC; Memphis, Tennessee; New Orleans, Louisiana; El Paso, Texas; Las Cruces, New Mexico; and Phoenix, Arizona.
One of the running gags in the series is Khufu, a baboon who is obsessed with basketball and only eats foods that end with the letter "O." He likes Oreos, of course, and Cheerios, and if he is eating meat, it's better not to ask where it came from, because things like chicken, turkey, pork, and beef, don't end in "O."
I do wonder how these books fit together in the chronology of Percy's universe. Do we never hear about Superstorm Typhon because Carter was traveling the world with his dad, and Sadie was in London and so it didn't impact them directly? Was it years ago and people have moved on by now? Has it not happened yet?