Half Lives by Sara Grant

NOW: Icie's parents gave her $10,000 in cash, a map of a top-secret bunker, and instructions to get there by any means necessary. They have news of an imminent viral attack and know that the bunker is Icie's only hope for survival. She and three other teens live locked away for months, not knowing what's happening in the outside world or who has survived. Then one day, Icie discovers a shocking secret deep in the bunker. Are they really safe there after all?

THEN: Generations in the future, the world has changed, and a mysterious cult worships the very mountain where Icie's secret bunker was built. The people never leave the mountain, they're ruled by Beckett, a teenager...and they have surprising ties to Icie.

Icie and Beckett must both fight to survive while protecting a secret that could destroy their civilizations.

This high-stakes, original, and thought-provoking adventure follows two unlikely heroes, hundreds of years apart.