"The Big Thinker" is a pleasant surprise, balancing a surplus of subplots centering on the attempted sabotage of a new super computer named 'Plato' (not to be confused with 'George Oblique Stroke XR40'). Anthony Booth plays Dr. James Kearns, the young genius looking after Plato, whose passion for poker gets him into trouble with Cathy Gale, posing as an anthropologist needing Plato's aid in studying dead languages. Working alone while Steed is supposedly off to the Middle East, Cathy keeps close to Dr. Kearns, as other members of the team fall victim to the unknown saboteur. The computer is not portrayed as a threatening presence, but does reveal the guilty party, whose final act results in his own electrocution (in effect, succeeding at the cost of his life). There is a welcome hint of jealousy as Steed discusses Kearns with Cathy, and a wonderful sequence where Cathy foils an attempt to cheat her out of 500 pounds by revealing how the villain shaved the card deck (Honor Blackman has a field day throughout). Steed inexplicably has a new dog named Sheba, which appeared in a total of five episodes (Freckles the Dalmatian was out after just two entries). Series veterans include David Garth ("How to Succeed....at Murder" and "Wish You Were Here"), Tenniel Evans ("Please Don't Feed the Animals," "The Golden Fleece," and "All Done with Mirrors"), Allan McClelland ("Build a Better Mousetrap"), and Ray Browne, previously seen as a murder victim in "The Sell-Out."