Vic is at a Stalag where captured Allied soldiers are being held, with Claude Akins an American sergeant being interrogated, but actually just impersonating a G. I. This is to fool Vic and the other prisoners into giving away useful information.
Primary goal is to discover which area has been chosen by the Americans for an upcoming attack on German lines. Akins is well-schooled, prepared for any question about American history or culture. Vic is wary, and the smart money (from the fans) is on him to figure out that Akins is an imposter, especially as Claude is overplaying his role on purpose.
Instead, a new prisoner notices the impersonation: he knows the real sergeant, recently missing in action, and tells Vic and his compatriots that Akins is not him. Now it's a race against time for Vic to escape and inform the Allies that the enemy has acquired vital intel about the upcoming attack.
With the rest of the cast of regulars not present, it's a one-off episode, with Vic underplaying in a story stressing less than credible plot twists but very low on the usual action/battle scenes.