The Xindi, ENT 3
Season 3 begins with a great setting (the Expanse), a clear goal (get the Xindi!) and some story-based reasons for T’Pol to try on new outfits (resigning her commission and Neuropressure sessions with Trip!) Heck, even the song has a little more pep.
I like the jailbreak aspect of this episode and learning more about the Xindi.