The Second Mona Lisa 

One year after three pilot shows were filmed, the series proper began production November 9, 1953, starting with episode 4, "The Second Mona Lisa," shooting all 23 in England through April 1954. In place of Ewan Roberts' Inspector Ames, Alan Wheatley receives co-star billing with Boris Karloff, a mystery since his O'Brien character never made a repeat appearance, an art dealer for The Florentine Gallery. Resembling an early episode of THE AVENGERS, O'Brien calls upon Colonel March to provide insurance for his upcoming sale of The Second Mona Lisa (painted six months after the first), one bidder being The Emir of a Middle Eastern nation (Eric Pohlmann), the other a Texas oil magnate, Wyatt (Robert Ayres), who wants to purchase it for his personal museum. O'Brien sends for Matthew Constable (Frederick Leister), the owner of the original, because only he can authenticate which is which, confirming that O'Brien's copy is the genuine article. Wyatt swiftly concludes the purchase, immediately returning to his hotel with his bodyguard Rogers (George Margo), only to have an intruder apparently pull a timely switch, as The Emir now proudly displays what appears to be the original on his own wall. It's up to Colonel March to ferret out the truth, vindicating O'Brien as the culprit is revealed. Eric Pohlmann makes his first of five appearances on the show, with the other four playing the same role, Inspector Goron of the French Surete, first seen in "Passage at Arms."