The CW has released an official description for “Missing” which is the next-to-last episode of Arrow Season 5.
Look for the episode on May 17. Here’s the write-up:
BLACK SIREN RETURNS — Black Siren (guest star Katie Cassidy) returns to help Chase (Josh Segarra). Felicity (Emily Bett Rickards) organizes a birthday party for Oliver (Stephen Amell) while Lance (Paul Blackthorne) is furious after Rene (Rick Gonzalez) misses the custody hearing for his daughter. Mairzee Almas directed the episode written by Speed Weed & Oscar Balderrama (#522). Original airdate 5/17/2017.