Penryn and the End of Days is a book trilogy by Susan Ee. It consists of Angelfall, World After and End of Days. Susan Ee has mentioned that this is "Penryn's story" and that other stories in this world may continue on after the series is over.
Penryn is trying to survive. After the angels destroyed the modern world, there are no rules. Streets are ruled by gangs and angels are hunting for humans. When her sister is kidnapped, Penryn will do everything she can to find her. Even if it means working with the enemy.