The Man from U.N.C.L.E. (1964)

S02E19 The Waverly Ring Affair

After secret documents labeled "File 40" are discovered outside the headquarters, Waverly tasks Solo and Illya with investigating whether George Donnell is a double agent. Carla Drosten hesitates to confront Donnell directly, so Solo employs the special "Waverly rings" to uncover the true identity of the real double agent.