Some good acting
It seems that this series has flopped, but meanwhile it showed us some good acting. I would single out the performance of Jonny Phillips as Whittington, the villain's chief henchman in "The Secret Adversary".
Phillips achieves what Ted de Corsia achieved in a similar part in The Enforcer (1951). As the late film critic Pauline Kael put it, "De Corsia, with his sinister accent and his humorlessness and impersonal anger, takes over as the star." The nominal star was Humphrey Bogart.
Phillips knows the art of delaying a facial expression just long enough to make us uneasy, and then more than justifying our fears. Of all the things happening on the screen, the one that commands the most attention is this performance. At least, one hopes it's a performance.