One of the attractions of The Avengers is the variety of story types: fantasy, espionage, science fiction, revenge, etc. This one falls solidly in the espionage category, featuring Tara King trying to breach the security of a top-secret government project. Why is she doing it, and who is she working for? Those questions drive the plot along, with the usual band of quirky secondary characters, including a villain who admires his own elegant feet, and an old lady who reads lips. There are plenty of standard spy tropes, including hidden cameras, and messages hidden in phone booths, plus a superbly choreographed fight scene at the end which may be the most acrobatically satisfying fight of the entire series. The final tag scene is classic Avengers, and is long enough to give you a good hearing of Laurie Johnson's "Tara" theme. Howard Blake, filling in for Johnson on the main score, does a seamless job of integrating with the standard "Avengers" sound, with the addition of what sounds like a Wurli electric piano. Don Chaffey (who directed some of my favorite PRISONER episodes) does an artistic job with interesting shots and angles.
I had not watched the Tara episodes for many years, and was expecting to be disappointed when I binged them recently. However, with only a couple of exceptions, these stories hold up well in the AVENGERS canon.