The Avengers - Season 1 - Eps 3: Square Root of Evil
Steed impersonates Riordan, a forger soon to be released from prison, and gains the trust of gang-leader Hooper. Things seem to be going well until Hooper's second-in-command, known as the Cardinal, announces that Riordan's girlfriend is outside waiting to see him.
About The Avengers

Title: The Avengers
First Air Date: 1961-01-07
Last Air Date: 1969-05-21
Status: Ended
Rating: 7.729/10 (from 140 votes)
Language: EN
Seasons: 7
Total Episodes: 161
Network: ITV1
Genres: Action & Adventure, Crime, Sci-Fi & Fantasy
Production Companies: Associated British Picture Corporation, Associated British Corporation, ABC Weekend Television
Synopsis
A quirky spy show of the adventures of eccentrically suave British Agent John Steed and his predominantly female partners. Jonathan Steed - an urbane, proper gentleman spy - teams with various assistants throughout the series' run, including Dr. David Keel, Cathy Gale, Emma Peel and Tara King, to repeatedly save the world from diabolical schemes plotted by equally diabolical evil-doers (among them robots and man-eating monsters).
Cast

Patrick Macnee
John Steed

Linda Thorson
Tara King

Ian Ogilvy

William Lucas