Janie, a single mom, shares a small apartment with her 4-year-old son. Kind of a harrowing premise already, right? Noah has always been a handful. He throws epic tantrums to avoid bathing, wakes up screaming at night and panics at the idea of being left with a babysitter. "It was just part of Noah's uniqueness." Like any mother, Janie is a little slow on the uptake when it comes to the apple of her eye. The thing is: He's creepy. The kid spouts facts on subjects he hasn't learned about and knows things about places he hasn't been. "When is my other mother coming?" he asks Janie. Noah's preschool is so freaked out by his increasingly bizarre behavior that Janie is forced to get him professional help. After visits to many doctors, Noah is offered a mental health diagnosis and medication. But Janie turns to a higher power: Google. And she comes across a theory that might explain everything. Could it be that her son is remembering a past life? Desperate, she reaches out to an eminent researcher, Dr. Jerome Anderson. This sounds ludicrous. And it shouldn't work. But Guskin pulls off the silly premise with a gripping, deft and moving mystery. Did Noah have a previous life? Was he murdered? And where is his "other mother"? Anderson has his own motives for studying Noah. Recently given a diagnosis of aphasia, he's racing to finish a book of case studies before the dementia takes hold. Noah remembers more than he should, Anderson less and less. They're both learning to let go. Chelsea Cain is the author of "One Kick" and other thrillers.