Newman builds on the best elements of her interconnected Planetfall series for this superb fourth volume (after Before Mars), which centers on a covert investigation into nuclear genocide. Emotionally cold Dee seethes, wondering who aboard the spaceship Atlas 2 ordered the secret nuclear launch that ravaged Earth. The only people who observed the detonation are Dee; her best friend, Carl; and Carl's "sort-of lover," Travis. Six months into their 20-year journey to a new world, an unexpected offer of a job analyzing entertainment usage allows her access to the ship's computer systems, which lets her seek answers. She is also invited to elite games where players rely on their real-world physical abilities in virtual space, and encounters a cagey virtual guide. After her first foray, she is disturbed that a man she killed in the game died in the real world. Carl, a former detective, investigates the man's death, but the mysterious guide uses impressive data hacking skills to stymie him and protect Dee, while inviting Dee to take revenge on the game's designers for setting her up to be a killer. Despite her fear of being caught, Dee agrees to aid the guide's scheme. Tense moments mount as she learns more about her incognito ally and the ship's leadership, leading to a chilling, ethically complex ending. This winning combination of intriguing mystery and inventive SF richly rewards Newman's longtime readers and will lure others to the series. Agent: Jennifer Udden, Barry Goldblatt Literary. (Apr.)