The Gathering — Will Peterson

After escaping the Australian Outback -- and the nefarious agents of the ill-named Hope Organization -- Rachel and Adam have fled to the United States in hopes of locating their father. Luck is evading them, however, until they follow the clues in the note their Granny Root left them, leading straight to a military base in Alamogordo, New Mexico. Meanwhile, their mother is facing charges of murder in Oklahoma, even as Dr. Laura Sullivan speeds to New Mexico to snatch the kids from the clutches of the Hope Organization. Will Rachel and Adam discover the third and final triskellion before it's too late?