Supergirl becomes Xenu, The Flash meets another DC fan-favorite, Legends visits another 80s film, and Arrow lets the characters switch seats.

(Synopsis cut and pasted from Trakt.com.)

Supergirl – The Faithful – Kara investigates a secretive new group whose leader, Thomas Coville, has a mysterious connection to Supergirl. Meanwhile, Samantha feels like she’s letting Ruby down, and J’onn confesses an old secret.

The Flash – Elongated Journey into NightJD covered this indepth.

DC’s Legends of Tomorrow – Phone Home – The Legends learn that Ray Palmer will die because they broke time, causing them to race back to 1988 to try and save his life. When they arrive, they are surprised to learn that young Ray Palmer has befriended a time-displaced baby Dominator putting him in harm’s way with the government and the Dominator’s mother. New to the ship and missions, Zari must find her place and learn to trust the team. Meanwhile, Stein begins working on a secret project on the ship which makes Rory and Jax suspicious.

Arrow – The Reversal – Just as Oliver starts to get things in order, Black Siren launches another attack on the citizens of Star City.