Home from their unexpected deployment, the former members of Marine Force Recon team Sidewinder rejoin their loved ones and try to pick up the pieces of the lives they were forced to leave behind. Ty Grady comes home to Zane Garrett, only to find that everything around him has changed—even the men he went to war with. He barely has time to adjust before his brother, Deuce, asks Ty to be his best man. But that isn't all Deuce asks Ty to do, and Ty must call for backup to deal with the business issues of Deuce's future father-in-law.

Nick O'Flaherty and Kelly Abbott join Ty and Zane at the wedding on an island in Scotland, thinking they're there to assuage Deuce's paranoia. But when bodies start dropping and boats start sinking, the four men get more involved with the festivities than they'd ever planned to.

With the clock ticking and the killer just as stuck on the isolated island as they are, Ty and Zane must navigate a veritable minefield of family, friends, and foes to stop the whole island from being destroyed.