“Thirteen” is episode seven of season three of The 100.
In the previous episode, “Bitter Harvest”, Raven had failed to find the upgraded version of Alie’s code in the Ark’s database. Jaha mentioned that there had been a thirteenth station, Polaris, which was destroyed. Murphy, having been captured, was being forcefully interrogated by Titus, whilst behind him was what looked to be an escape capsule with the letters P O L I S visible, with a large space between the L and the S – obviously ‘POLARIS.’
Murphy was being questioned over his possession of the tablet given him by Jaha that would reveal the City of Light. The tablet has an infinity sign on – according to Titus, this is the holy symbol of the Grounders (and ‘Polis’ has been mentioned before). According to Murphy, it’s a corporate symbol.
Events then go back 97 years previously, just before the war. A scientist, Beka (played by Erica Cerra, the same actress as Alie), is working on a new AI, the second generation of it as there were problems with the first. These problems quickly become known as she is contacted and informed that Alie, the first generation, has escaped onto the Web and is hacking nuclear launch codes. Beka is working on a space station, Polaris, and the nuclear destruction quickly unfolds on the planet below. This past returned to a couple of times within the episode, especially on Unity Day, when Polaris was reputedly destroyed.
On Lexa’s Ascension Day, Octavia is brought before her as those of Trikru who captured her tell Lexa about the attack on their village. They want vengeance. The Commander does not give them simple vengeance, but instructs the clans to surround Camp Arkadia at a distance of five miles, and a kill order is given to any of Skikru who are found outside that perimeter after it is formed. Clarke has convinced Lexa that Skikru will eventually overthrow Pike, and to give them time to do so, but she is less pleased about the kill order.
Titus is loyal to Lexa, but he manifestly doesn’t approve of her actions, although this disapproval is mostly kept quiet as he publicly supports her, and defends her. His determination to protect Lexa from the consequences of her actions leads to unfortunate consequences in itself.
Some revelations about what happened at the time of the war, on Unity Day, and where Alie 2.0 got to. Nothing from Arkadia and the others this episode.