Dark Waters

"As today's tragedy has reminded us, we are at war. For 6 months, we have been besieged by a nameless and a faceless organization that seems hell bent on destroying our city. You know them as the Ghosts. And while they may be anonymous, their leader is not. He has a face, he has a name, and I think that it is high time the people of Star City know the truth about who he is. His name is Damien Darhk. He controls the Ghosts on behalf of an organization known as HIVE. HIVE wants this city to die."

- Oliver Queen's televised message to Star City and Damien Darhk "Dark Waters" is the ninth episode of the fourth season of Arrow and the seventy-eighth episode overall.

Synopsis
After the city is attacked again, Oliver makes a bold move against HIVE. Malcolm checks in on Thea and leaves her with a warning. Things take a horrible turn when Damien Darhk retaliates in a brutal manner at Oliver’s mayoral holiday party.

Plot
Oliver encourages citizens to clean up the bay, prompting Darhk to send a drone attack. Felicity takes it down, but many are injured. In retaliation, Oliver reveals Darhk's photo, declaring him the leader of the Ghosts, on television and sets up a hotline for anyone who has any information about him. Darhk, watching on television with other HIVE members, is visibly enraged and breaks the television with his magic. Milo Armitage makes a sarcastic remark. Reluctantly, they go through with a Christmas party to show they are not afraid. Andy Diggle continues to be uncooperative with his brother Meanwhile, Felicity's mother discover's Oliver's engagement ring and shows her daughter. At the Christmas party, Felicity learns that her mother is dating Quentin Lance. Later, she and Oliver meet Curtis's husband. During their discussion, Felicity realizes Oliver was going to propose the night Laurel and Thea came to get their help. Felicity asks Oliver why and he says that everything changed and he wasn't sure he could anymore. Darhk breaks in despite high security, knocks out Oliver, and kidnaps Diggle, Thea and Felicity. Oliver and Laurel go out to beat on the Ghosts to get a location, but come up with nothing. Malcolm arrives in the Arrowcave, surprising Quentin, and provides a communicator that the Ghosts use. Oliver offers himself up to Darhk, who takes him back to HIVE HQ. Laurel and Malcolm, who is dressed as the Green Arrow, follow, using a nanotracker in Oliver's bloodstream. Darhk demonstrates algae that HIVE is growing in the bay, which they are trying to adapt to make breathable. They test it on humans, who they put in a gas chamber. He lets Oliver have one last conversation with Felicity who says she would have agreed to marry him. Darhk decides that, although Oliver is agreeing to work with him now, it is easier to remove all motivation for resistance and kill Thea, Diggle, and Felicity in the gas chamber. Laurel and Malcolm arrive, with Laurel's Canary Cry breaking the glass and freeing the captives. The other members of HIVE escape, while Malcolm and Oliver go after Darhk. After a fight, Malcolm leaves Damien pinned to the ground with arrows and right next to an exploding arrow. Quentin and a squad of cops help the others escape from the many HIVE pledges and later Oliver holds another tree lighting where he proposes. As the new fiances return home, their limo is attacked by Ghosts. The driver is killed and Oliver leaves Felicity in the back as he drives them to safety. Meanwhile, Damien enjoys decorating his Christmas tree with his wife and young daughter. Oliver opens the door of the limo and finds an unresponsive Felicity with a slight of blood coming out of her mouth.

Production
Preparation ran from October 5 until October 14, 2015. Shooting ran from October 15 until October 27, 2015.

Trivia

 * Oliver finally proposes to Felicity; however, he seems to have forgotten or disregard the fact that cannot marry Felicity, as he is still technically married to Nyssa al Ghul, albeit under the name Al Sah-him, as the public is not aware of this.