"Thirteen" focuses largely on Lexa and on Polis. We know that Semet is outraged that Lexa is not calling for war against the Sky People, but how many others feel as Semet does? Either way, we are very worried about Lexa's fate right now.
The motives of Lexa's advisor -- and what exactly he knows about the Polis/Polaris connection -- are still unclear. Is he truly looking to protect Heda, or are his motives in calling for destruction of the Sky People much more nefarious? This ambiguity makes Titus one of the most intriguing characters on the show.
Octavia's gag is removed here, indicating that she's at least been allowed to speak her piece and explain her side of the story. It seems unlikely that Lexa will misconstrue Octavia's motives and punish her for her interference -- it's clear that Lexa and Octavia both strive for peace above all.
Lexa stands over Titus, demonstrating her superior position over him. Lately, Titus has been exceedingly vocal in his disagreements with Lexa over how she chooses to rule, causing tension between the Commander and her advisor.
Poor Octavia. She was just trying to do the right thing by everyone -- warning the Grounders of the impending attack and warning Skaikru of the Grounders' counterattack -- and instead she is now an enemy of all.
Various members of the thirteen clans gather around Lexa on her throne, likely to hear the discussion of the fate of Octavia (now Semet's prisoner). Clarke lingers to the side and Titus hovers near Lexa.
Lexa: My fight is over. Clarke: No, I won't accept that. Lexa: You were right, Clarke. Life is about more than just surviving. Clarke: In peace may you leave the shore. In love may you find the next. Safe passage on your travels until our final journey on the ground... May we meet again.