The last several episodes of "Star Trek: Enterprise" have all been like one long movie--not the usual self-contained episodes. They all tell the story of what happens when the ship finally reaches the Xindi ultimate weapon and how the humans and Xindi somehow make peace.
This particular episode features two of the Xindi species (the most human-like by the way) spending time with Captain Archer and discussing a possible peace between everyone. However, it's obvious that the Reptilian Xindi are rather insane and warlike and would LOVE to vaporize the Earth. What also soon becomes obvious is that some of the crew hate the Xindi and just want to kill them--Trip, of course, being among them because of the murder of his sister by their first weapon. Despite this, Degra makes a fateful decision-- one that definitely makes a HUGE departure of the humanoid Xindi from the alliance.
All in all, like all the recent episodes, this one is full of action and tension--and make it among the best episodes of season three. Exciting and well worth seeing.