A former marine and CIA agent, Harrison Goodsell, is found tortured and murdered on NCIS: Los Angeles Season 6 Episode 8. He's believed to be a homeless man suffering from PTSD because that's what Granger tells the team. Hetty is kept off the case by Granger due to what happened in Afghanistan, but as normal she can't help it and gets involved.
Granger was keeping the truth from the team. Goodsell went AWOL from the military and wasn't homeless. He was working a case as a homeless man. Kensi and Deeks find out he also dressed up in a suit to have lunch in a restaurant. The clues lead them to the Mexican cartel leader, Pena, who was being extradited to Los Angeles.
The team believes the cartel is trying to stop Pena's extradition. They follow leads and find out the prosecutor, Kevin Turner, is missing. They find him at his home being held captive. NCIS takes out the Mexicans holding him and bring him in for questioning. At the same time, NCIS questions a CIA asset.
The team gets it all wrong. They let Turner go, but he was the one tasked with killing Pena. His girlfriend and daughter were held as collateral. They would be killed if Turner didn't kill Pena. Sam and Callen stop Turner, while Kensi and Deeks save the hostages. Goodsell got involved because he was Turner's father, only the prosecutor didn't know it.