Why did they come? When they appeared across the sky, speculation wheeled around the world—the aliens were from heaven, the invaders were from hell… or they were proof that neither existed. But when they landed, curiosity gave way to suspicion and the nations reacted with nuclear force, setting off a chain reaction that left the world in ruins. Twenty years later, instead of nearing her retirement, Dr. Elspeth Darrow struggles to forget the loss of her child and husband by plunging herself into the work of operating the last remaining hospital in San Francisco. With medical supplies running out and working herself to exhaustion, Elspeth must embark on a risky salvage mission into the heart of the Neo California danger zone. Here, she discovers the disturbing truth: the aliens have returned. As the mystery of the aliens' purpose on Earth unravels before her, Elspeth must hide what she discovers from reactionary despots, all vying to bring Neo California under their control. Aided by a band of pre-war scientists and new-world medical students, Elspeth races against astronomical odds to reveal the terrifying truth that might save the world—or finally destroy it for good.