Plot summary
Murphy convinces Titus to tell him more about the origin of his religion, speculating that the first Commander was from the 13th station rather than born on the ground. Flashbacks to 97 years earlier reveal that after A.L.I.E. causes the nuclear apocalypse by hacking all of the world's computer launch codes, Becca – A.L.I.E.'s creator and avatar template – attempted to create A.L.I.E. 2.0 to interface more directly with humanity. When the Ark destroyed her research station Polaris, Becca injected herself with an unknown black substance while implanting the A.L.I.E. 2.0 in her neck, and traveled to Earth in an escape pod.
In the present, Clarke and Lexa sleep together for the first time as they prepare to part ways in response to Lexa's decision to blockade Arkadia until Pike is removed from leadership. Titus attempts to ensure that the Sky People are destroyed by shooting Clarke and blaming Murphy for it, only he shoots Lexa accidentally. After Lexa dies, it is revealed that the A.L.I.E. 2.0 computer has been implanted in the back of her neck; Titus describes it as the spirit of the Commander.
Credits
Adapted from Wikipedia contributors, List of The 100 episodes. HTML formatting and reference markers removed.