It was first broadcast in the UK on ITV (ATV Midlands and Grampian) on Friday 29 September 1967, and first aired in the United States on CBS on Saturday 1 June 1968.
An unidentified British intelligence agent storms into his employer's London office to hand in his resignation.
He discovers the Village is surrounded by mountains save for its beachline, which opens onto the ocean with no sign of land nearby.
At the Green Dome, where several technicians monitor all aspects of the Village, Number Two tells the man they only wish to know why he resigned and to whom he is loyal, as the intelligence he has gathered over his career is too valuable to simply let him "walk away".
Number Two takes the man on a tour of the Village to show him the security systems they have in place to keep the inhabitants in line, including Rover, a mysterious floating balloon guardian that attacks those who flee.
Number Six attends Cobb's funeral and observes a woman watching from afar, and proceeds to follow her around the Village before he talks to her directly.
Further scenes were shot on 6 September, but Guy Doleman (playing Number Two) was suffering from cracked ribs and his presence only lasted two days.
On 30 September, the last day of shooting at Portmeirion, McGoohan directed a number of shots including Rover's attack on a Villager in the main piazza.
All of guest stars George Baker (new Number Two) and Paul Eddington (Cobb) were shot in this period.
A key set was redressed as Number Two's living quarters, the Control Room and the Labour Exchange.
His score and theme tune was rejected, and Wilfred Josephs was commissioned to write another in early January 1967.
Ron Grainer was asked to create a theme tune and his was later used on all episodes, a longer version prepared for the extended opening sequence in "Arrival".
[1] During the production of the last four episodes of The Prisoner series (the episode "Living in Harmony" was being made) ITC arranged for a press conference to take place at MGM-British studios in Borehamwood on 20 September 1967 – a week before the scheduled transmission on some British TV channels.
At the press coverage Patrick McGoohan (at the start wearing his kosho uniform, a made up martial art used in the series) was interviewed inside the cage shown in the episode "Once Upon a Time".
Both episodes had different title sequences at start and finish to that eventually broadcast, as well as with different theme music (by Albert Elms rather than Ron Grainer) and different edits of scenes including different shots and extra dialogue.
A 2007 DVD release included an improved-quality version, digitally remastered from a faded 35mm print, which can also be viewed with a music-only soundtrack.