Robert "Bobby" Trench (Washington) and Michael "Stig" Stigman (Wahlberg) are questioned by the US Border Patrol after meeting with drug lord Manny "Papi" Greco (Edward James Olmos) in Mexico. Unknown to Stig, Bobby is undercover DEA agent Trench who reports to his superior, Jessup (Robert John Burke), that he didn't get the cocaine from Papi they need to convict him.

Against orders, Bobby remains undercover to assist Stig in robbing $3 million - in a bank vault in Tres Cruces, Texas - to prosecute Papi for money laundering. Bobby then meets with fellow DEA agent and ex, Deb Rees (Paula Patton), while Stig, an undercover Navy SEAL with ONI, meets with his commanding officer, LCDR Harold Quince (James Marsden), and is told to kill Bobby so they can fund covert operations.

Bobby and Stig are surprised to find $43.125 million and not $3 million. Stig follows orders to betray Bobby and escape with the money, pulling his gun as Bobby is about to pull his. Stig wounds Bobby in the upper arm rather than kill him, and then sees Bobby's DEA badge. Unsure what to think, Stig leaves him in the desert.