"Colony Three" "The Carriers" is one of the best episodes of "Mission: Impossible"--with a great plot and a nice guest appearance by George Takei. Takei's appearance isn't surprising, as the same studio was producing both "Star Trek" and "Mission: Impossible" and William Shatner and Leonard Nimoy also appeared in both of the shows.
The Impossible Mission Force is sent to infiltrate a Soviet city that was built to be inhabited by spies preparing to be sent to blend in with Americans. To do this, the town is an exact replica of a town in the US and everyone is ordered to speak English and act as if they are really living in the States. However, although the stated purpose of this town is to train agents to blend in seamlessly, there is a much more nefarious reason for the compound--and the team must find that reason and neutralize it.
The idea of a Russian town made to look EXACTLY like an American town and inhabited by spies in training is very intriguing. It also is a very tense episode and kept my interest throughout. I noticed some complaints in other reviews about plot holes, but this didn't bother me. After all, it isn't like "Mission: Impossible" is an ultra-realistic series!! It's just escapist fun.
By the way, this show was probably inspired by the British series "Secret Agent". In "Colony Three" agent Drake infiltrates a similar town, though it's an exact match for a British town instead. However, the way the show plays out and ends is quite different.