Answer
The answer to the question of Arden's starring episode in the CBS show "Checkmate" is "Death by Design." This particular episode showcases the character of Arden, played by Doug McClure, as he becomes entangled in a complex murder investigation fueled by a missing necklace and a series of cryptic messages. The episode not only highlights McClure's talent but also provides viewers with a captivating blend of mystery and intrigue.