Nightfall (Unity episode)

"Nightfall" is the thirteenth episode of season six and the first of a three-part story.

''Exploring uncharted space, the starship Odyssey makes first contact with Devizes: a technologically advanced planet with an unsettling origin. Diplomacy soon switches to survival when the ship is invaded, as Mitchell's growing desire to return home brings him face-to-face with Puto and Lewis' oldest enemy...''