Semper Fi tells the story of Courtney as Cal, a by-the-book police officer who also serves as a Marine Corps reservist alongside his rowdy group of childhood friends.
When Cal's younger half-brother Oyster accidentally kills a man in a bar fight and tries to flee, Cal forces him to face the consequences.
After an unfair sentence, Oyster struggles to survive in a dangerous Pennsylvania prison while Cal and his friends are deployed to fight in Iraq.
Overseas, Cal's world is turned upside down, and he barely makes it home alive. Determined to help his brother, Cal resolves to break Oyster out of prison at any cost.