Light Riders and the Missouri Mud Murder (Light Rider Novels)

Sixteen-year-old Ryn and his younger sister, Aeden, hadn't planned on using their knowledge of time travel to solve any more murders. But when the body of their friend's great-grandfather turns up encased in mud, they decide to tackle one more mystery. Unaware that solar flares would interfere with the time-space continuum, the siblings find themselves caught in a time loop between 1952 and the Ice Age and are forced to use survival skills they never thought they had. But worst of all, someone has traveled back in time with them, posing a greater threat than any of the prehistoric animals they face. "Light Riders" Ryn and Aeden must work frantically to unlock the clues, because the next jolt through time could be their last. And this time, Snell's Law of Refraction won't save them.