When rookie astronomer Irina Kirilenko discovers a planet-size comet in the Kuiper Belt on a collision course for Mars, she first faces stonewalling from the Minor Planet Center, then coercion and stricture from NASA. They press her to embrace an ingenious reinterpretation of her discovery and ban her from talking about it. It slowly dawns on her that the government is fostering a massive conspiracy to keep the public oblivious to the truth—Earth is facing an existential threat.

Astronaut Lee Rifkin's life is about to change. NASA has done the math. The space object named Cassandra 22007 is not behaving as expected. He will lead a team on a cutting-edge ship to get a closer look. But another group wants to get there first. Who is this shadow organization that seems to be one step ahead of them? Agent Jenna Haynes works to put together the pieces that will pull the veil off those who seem to have known about Cassandra's arrival since long before NASA spotted it. What is their goal?

Propulsion scientist Dr. Todd Cunningham was an astronaut headed for outer space until budget cuts killed the mission—and his lifelong dream. Now, he's just an obscure expert in fusion-powered space travel, a professor buried in an ever-increasing pile of work. But when a daring mission is approved to travel to Europa, Jupiter's frozen moon, Cunningham is thrust back into the spotlight by the very man he blames for ending his NASA career, and he finds himself joining the ranks of NASA astronauts on a groundbreaking journey to challenge humanity's understanding of life in the universe.

The year is 2072. At the lunar farside radio observatory, an old school radio broadcast is detected, similar to those broadcast on Earth in the 1940s and early 1950s, but in an unknown language, coming from an impossible source, and originating at an equally impossible location—Proxima Centauri. While the nations of Earth debate making First Contact, they learn that the Proximans are facing an extinction-level disaster, forcing a decision: Will Earth send a ship on a multiyear trip to provide aid?

Scientist Beth Darlow has discovered the unimaginable. She's built a machine that allows human consciousness to travel through time—to any point in the traveler's lifetime—and relive moments of their life. An impossible breakthrough, but it's not perfect: the traveler has no way to interact with the past. They can only observe. After Beth's husband, the co-creator of the machine, dies in a tragic car accident, Beth is left to raise daughter—and continue the work they started. Mired in grief and threatened by her CEO, Beth pushes herself to the limit to prove the value of her technology.