About the only genre that Thames Television didn't have had to be a Western. They seemed to have everything else.
That includes spy dramas. Callan, which launched in 1967, ran for 4 "series" of varying length, totaling 43 episodes. For viewers here in the US, it was an introduction to Edward Woodward, who essayed the title role, and would later top-line an American drama, The Equalizer, in the 80's.
Callan's basic concept saw the title spy walking away from The Section, which might be a darker version of, say for example, the CIA here in the US. Part of the reason Callan quit was because he had become interested in learning about the targets he'd been assigned to kill. It's not quite unlike Patrick McGoohan's seminal psychological drama for ITC, The Prisoner, which ran for one series around the same time that Callan launched.
Let's take a look at the 3rd season episode, "The Same Trick Twice":
The series' coda actually came with the 1981 TV-movie, "Wet Job". Some episodes are available on DVD, depending on where you look.
No rating. Didn't see it when it aired on WOR.