A low key, but absorbing, TV series of half-hour episodes, it is the first of three putatively related series, the latter two being (a) Secret Agent Man (hour long episodes), and (c) The Prisoner.
In the series, our protagonist John Drake (played by Patrick McGoohan) is an English spy - elegant, skilled, sophisticated, and never at a loss. He breezes through his weekly problem, and we enjoy every second of the short ride!
In my opinion, the series was the undisputed master of its era, and I loved its whimsy, its thoughtfulness, and good plot lines, simply and starkly delivered. The later Harry Palmer movies (with Michael Caine - for example, The Ipcress File) was reminiscent of this same style - austere story line, strongly built around its main character, employing few cinematic effects, yet full of impact.
It has been years since I have seen this series, but it it is still one I remember very fondly.