Gillian Seagret doesn’t listen to people who say her father’s a crackpot. His conspiracy theories about the lost technology of Cold War-era rocket scientist Dr. Aloysius Underberg may have cost him his job and forced them to move to a cottage in the sticks, but Gillian knows he’s right and plans to prove it.

When she discovers a missing page from Dr. Underberg’s diary in her father’s office, she thinks she’s found a big piece of the puzzle—a space-themed riddle promising to lead to Underberg’s greatest invention. Enlisting the help of her brother, Eric, her best friend, Savannah, and Howard, their NASA-obsessed schoolmate, Gillian sets off into the ruins of a vast doomsday bunker deep within the earth.

But they aren’t alone inside its dark and flooded halls. Now Gillian and her friends must race to explore Omega City and find the answers they need. For while Gillian wants to save her dad’s reputation by bringing Dr. Underberg’s secrets to light, others will stop at nothing to make sure they stay buried . . . forever.

• An Unlikely Friendship: To solve the riddle, Gillian must team up with her skeptical brother Eric, her popular best friend Savannah, and the school’s biggest NASA nerd, Howard.
• A High-Stakes Quest: The mission: venture deep into a vast, flooded doomsday bunker to uncover a legendary invention and restore her father’s reputation.
• A Secret Underground City: Omega City is filled with forgotten technology and dangerous secrets, but Gillian and her friends aren’t the only ones exploring its dark halls.
• Lost Technology: They’re hunting for Dr. Underberg’s greatest creation, but a shadowy group will do anything to make sure it stays buried forever.