Paul and Frank thought with the death of Matthias, they had Final Closure. But they realized they were missing someone, the mastermind. They didn't believe they had everyone, and no one was talking.

The Fifth Man is a sequel to Final Closure. Paul and Frank look for the the puppet master.

Meanwhile, Chai has his new job and sets up his new undercover team. They find the first cases are not only linked, but linked back to the Matthias case, and further to early Thai Diamond History.

Diamond Detectives cut their teeth on new cases, but everyone wants the Fifth Man. The problem is, even though they become certain of who it is, how do they prove it in a court of law. Karen suggests the Bratislava solution.