Caught — Margaret Peterson Haddix

Jonah and Katherine are accustomed to traveling through time, but when learn they next have to return Albert Einstein's daughter to history, they think it's a joke -- they've only heard of his sons. But it turns out that Albert Einstein really did have a daughter, Lieserl, whose 1902 birth and subsequent disappearance was shrouded in mystery. Lieserl was presumed to have died of scarlet fever as an infant. But when Jonah and Katherine return to the early 1900s to fix history, one of Lieserl's parents seems to understand entirely too much about time travel and what Jonah and Katherine are doing. It's not Lieserl's father, either -- it's her mother, Mileva. And Mileva has no intention of letting her daughter disappear.