Whether the show's failure to find an audience in the US was a result of audience reaction or the manoeuvrings of TV execs is uncertain, what is clear is that television in the US was moving into less dangerous territory. Successful shows like The Man from Uncle were being softened up, partly through the influence of mid-sixties camp, partly through concerns over the depiction of violence. McGill's world of casual violence and moral ambiguity might be too grim for a nation seeking respite from the reality of the Vietnam war, who knows?
The single episode that really stick is my mind is, The Girl Who Never Was, this episode features Bernard Lee in a fantastic role. He plays a retired army man, Kershaw, I'm not sure what rank but his character's affectations suggest a Warrent Officer. Kershaw's character is brilliantly and succinctly conveyed in the script by Lee's performance. He's a man with his best years behind him, who misses the status and respect his rank afforded him. He's one of two antagonists in the story, the other, Gilchrist is an art dealer played by Annette Carell, while not exactly unscrupulous, Gilchrist is callous and devious and betrays both Kershaw and McGill in like manner.
The plot revolves around a painting looted from Italy during the war by a mentally disturbed British soldier and the efforts to recover it. McGill's character moves through the narrative like the wind or the tide, a force of nature, not a typical protagonist motivating the narrative, he just does his job. What makes his character sympathetic is his ethical code and his personal integrity. He doesn't meter out justice or arbitrate between good an evil, he's just trying to make an honest living while making as small a wake as possible through a sea of troubled humanity. As you might guess the resolution of the plot is not straight forward but the final scene is one of my favourites of any tv drama.