The Red Pyramid by Rick Riordan

Since their mother’s death, Carter and Sadie have become near strangers. While Sadie has lived with her grandparents in London, her brother has traveled the world with their father, the brilliant Egyptologist, Dr. Julius Kane. One night, Dr. Kane brings the siblings together for a “research experiment” at the British Museum, where he hopes to set things right for his family. Instead, he unleashes the Egyptian god Set, who banishes him to oblivion and forces the children to flee for their lives. Soon, Sadie and Carter discover that the gods of Egypt are waking, and the worst of them--Set–has his sights on the Kanes. To stop him, the siblings embark on a dangerous journey across the globe -- a quest that brings them ever closer to the truth about their family, and their links to a secret order that has existed since the time of the pharaohs.