The 100 airs a crucial episode, "Thirteen," Thursday night – one that offers a lot of insight into the show’s backstory and mythology.

The 100: "Thirteen" Photos 11 IMAGES

As The 100’s executive producer and showrunner, Jason Rothenberg, explains, “We tell a flashback to 97 years ago and we see the origin story of the show. We see what happens to the world and why the apocalypse happened.”Thanks to those flashbacks, there's good deal of outer space-set material in “Thirteen,” and as Rothenberg noted, by the end of it, “We understand the origin of the Ark, which had become a home for our heroes as the series began, three years ago."He added, "I love the idea that telling that story and the story of the two AIs is also the origin story for the show.”All of this is intermixed with a story in the show’s present, as Octavia (Marie Avgeropoulos) is brought to Lexa (Alycia Debnam-Carey) in Polis, as a prisoner of war – leading to some big decisions needing to be made on the escalating situation between Arkadia and Polis, with Clarke (Eliza Taylor) and her conflicting loyalties caught in the middle.Said Rothenberg, “It’s a big episode and an emotional episode.”

The 100: "Thirteen," airs Thursday, March 3rd at 9:00pm ET/PT on the CW.Eric Goldman is Executive Editor of IGN TV. You can follow him on Twitter at @TheEricGoldman , IGN at ericgoldman-ign and Facebook at Facebook.com/TheEricGoldman