The CW has released an official description for the next-to-last episode of Arrow Season 4, scheduled to air on May 18, 2016.
The episode is called “Lost in the Flood” and here’s how The CW describes it:
OLIVER FIGHTS FOR THEA; DONNA SMOAK FACES OFF WITH NOAH KUTTLER – Following the shocking events in the previous episode, Oliver (Stephen Amell) and Diggle (David Ramsey) race to rescue Thea (Willa Holland), while Felicity (Emily Bett Rickards), Curtis (Echo Kellum) and Noah (guest star Tom Amandes) join together to stop Darhk (guest star Neal McDonough). Glen Winter directed the episode written by Brian Ford Sullivan & Oscar Balderrama (#422). Original airdate 5/18/2016.