Another must-see episode that the series absolutely had to do, and part of the Terra Prime Duology that many fans believed made a better finale than the actual one.
After all the work done during the season building the foundation of the Federation, we finally return to the ugly xenophobia suggested in "Home" (which might be considered the real season premiere), which was in part suggested by the Xindi crisis from the previous season. So yes, there's a lot of material to support the developments of this story, but it also begs the question of whether or not Enterprise should have had more of it.
A character by the name of Colonel Green referenced in the original series episode "The Savage Curtain," is partly the inspiration for the story, in which his ideological successor John Frederick Paxton takes the reins and ups the ante by involving Trip and T'Pol, just in case they haven't been on enough of a violent emotional roller coaster this season. Meanwhile Reed is compelled to use his Section 31 contacts, and Mayweather runs into an old girlfriend (which becomes more relevant next episode).
Maybe none of that sounds enticing enough, but the second act makes the whole thing stronger, so stick around...
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Memory Alpha summary.