Underneath

"We're trapped."

—Felicity realizes Adrian Chase trapped her and Oliver in the Arrowcave.

"Underneath" is the twentieth episode of the fifth season of Arrow, and the one-hundred-twelfth episode overall. It aired on May 3, 2017.

Synopsis

Things get intense when Oliver and Felicity are trapped in the bunker together. Meanwhile, Lyla and Diggle deal with their martial issues.^[1]

Arrow 5x20 Promo "Underneath" (HD) Season 5 Episode 20 Promo

Arrow Underneath Trailer The CW

Arrow Inside Arrow Underneath The CW

Arrow 5x20 Sneak Peek "Underneath" (HD) Season 5 Episode 20 Sneak Peek

In Southern California, this episode along with The 100 episode "Die All, Die Merrily" were both postponed to May 6 due to coverage of the Giants/Dodgers game.
The flashbacks in this episode takes place between "Schism" and "Legacy".
This is the first episode of Arrow to not feature a main (human or otherwise) villain, nor does it involve other villains (although Adrian Chase appears at the end interacting with Oliver's son, William). Instead, Team Arrow faces the Arrowcave, which acts metaphorically as a "villain"; an EMP set off by Chase disabled the base where Oliver and Felicity are trapped, so Diggle and the rest of the team must rescue them before the air in the Arrowcave runs out.
Curtis refers to his T-Spheres as Kodo and Podo, naming them after "Dar's thieving ferrets on The Beastmaster". He also mentions former Arrow recurring actor Marc Singer, who portrayed Dar in the film.
Curtis refers to an "Earth-shattering kaboom", quoting the catchphrase of Looney Tunes character Marvin the Martian.
Curtis says that it will take "10 seasons of The Bachelor" for the hydrochloric acid to melt through the titanium hinges of the elevator.
When Curtis' T-Sphere opens for Felicity to reveal a needle, she quips that it looks like the "Death Star interrogation droid" from Star Wars: Episode IV – A New Hope.

Preparation ran from February 23 until March 3, 2017. Shooting ran from March 6 until March 15, 2017.^[2]

Arrow season 5
"Legacy" • "The Recruits" • "A Matter of Trust" • "Penance" • "Human Target" • "So It Begins" • "Vigilante" • "Invasion!" • "What We Leave Behind" • "Who Are You?" • "Second Chances" • "Bratva" • "Spectre of the Gun" • "The Sin-Eater" • "Fighting Fire With Fire" • "Checkmate" • "Kapiushon" • "Disbanded" • "Dangerous Liaisons" • "Underneath" • "Honor Thy Fathers" • "Missing" • "Lian Yu"