SPOILER WARNING: This article contains major spoilers for "Fundamentals," the latest episode of Arrow.
Prometheus has returned to Arrow -- kind of. In "Fundamentals," the latest episode, Oliver Queen was dosed with Vertigo by Councilman Kullens, one of his political rivals. The ensuing hallucinations brought Adrian Chase back into his life.
As he prepared for his impeachment hearing, Oliver returned the bunker, where he contemplated his next move. After a moment, he heard a loud banging sound, and then the elevator began to move. He grabbed a gun and stood waiting for his uninvited guest, who turned out to be Adrian "Prometheus" Chase.
The two came to blows, but the fight ended with Chase in a headlock. Chase taunted him, saying that Oliver would never be able to truly kill him and threatening to come after Felicity and William next. With a look of regret, Oliver then cracked his back and dropped him on the floor -- only for Chase to pop up beside him moments later.
Oliver quickly deduced that he was hallucinating. After a blood test, he discovered he had Vertigo in his system. He realized that he had begun to experience symptoms after his meeting with Kullens, which led him to put two and two together: he was being sabotaged by another corrupt government official. Thus, he began hallucinating Adrian Chase.
Chase stuck around for the duration of the episode, goading Oliver about the loss of his teammates and friends. He led him through a series of memories, from the day he set out on the boat that sunk near Lian Yu to Laurel's death. Chase also plagued him throughout his impeachment hearing, which he bombed spectacularly, leading him to be ousted from office.
Ultimately, Chase persuaded him to take on Ricardo "The Dragon" Diaz alone. In a back-to-basics move, Oliver put on his original Arrow costume and set out for the police station, knowing that Diaz would be there because of information uncovered by Felicity earlier in the episode. Quentin tried to stop him, but Oliver swiftly knocked him out. Fortunately, Felicity made it there just in time to convince him to stop. They were able to escape just in time.
Though Josh Segarra's Prometheus returned for the episode, it's doubtful we'll see him again, since he was a product of Oliver's subconscious. However, another dead character is in the lineup: Tommy Merlyn. Earlier this week, Collin Donnell revealed that he would reprise the role, but offered no further details.
Starring Stephen Amell as the Emerald Archer, Arrow airs Thursdays at 9pm ET/PT on The CW. The series also stars Emily Bett Rickards, David Ramsey and more.