They're too old for this fight... but they're the only ones left standing.

When the Colonial Shield Federation needs someone to face an ancient alien threat, they don't call their best; they call the only two Marines who survived first contact. Problem is, a decade of hard living has taken its toll on Frank Cage and Martin Kelvin. Frank has spent the last ten years drowning his memories in whiskey and starting bar fights, while Martin walks around on a cybernetic leg, tending his garden and trying to forget the past.

But their retirement comes to an abrupt end when a military transport arrives, crushing Martin's prized tomatoes and bringing orders that can't be refused. It seems the Hollow have returned...

Forced back into now-outdated power armor and paired with a squad of combat-tested scientists who think they know the enemy better than the people who fought them do, these two grizzled veterans must face something far worse than death.

Because the Hollow don't just kill; they collect. In the depths of a long-buried facility, Frank and Martin will quickly find out if they still have what it takes to survive—and what it will truly cost them.

The first book in this high-octane military sci-fi saga marks the explosive start of an exciting collaboration between USA Today-bestselling author J.N. Chaney and New York Times-bestselling author Nicholas Sansbury Smith that's perfect for fans of Expeditionary Force and Undying Mercenaries.