Starring and co-created by Patrick McGoohan, it combined spy fiction with elements of science fiction, allegory, and psychological drama.
The series follows a British former secret agent who is held prisoner in a mysterious seaside village where his captors try to find out why he abruptly resigned from his job. Although sold as a thriller in the mould of McGoohan's previous series, Danger Man (called Secret Agent in its U.S. release), the show's combination of 1960s countercultural themes and surreal setting had a far-reaching effect on science fiction/fantasy programming, and on popular culture in general.
The series features striking and often surreal storylines, and themes include hypnosis, hallucinogenic drug experiences, identity theft, mind control, dream manipulation, and various forms of social indoctrination. A major theme of the show is individualism versus collectivism." (WikiPedia)
I just recently started watching this series, and I must say it's great! The plot built around the main character, number 6, is kept very consistent, each episode reveals some minor details about him, the mysterious Village and it's leaders. Even though the special effects are very outdated and often rather funny, the story is still very entertaining.
If you're into mystery-series', I definitely recommend checking out the Prisoner!