Just a little something that I've been meaning to get to or a while after a conversation with Philippe363. For timeline wise, this takes place at some point after 5x12. Enjoy.

Oliver Queen's apartment

Might

Oliver walked into his apartment, releasing a weary sigh after a long day. He tried to flip the lights on but frowned when nothing happened. Having practically invented this move, Oliver cautiously walked into the kitchen. Sitting in a chair was a dark skinned man in a leather jacket wearing sunglasses.

"Mr. Queen," the man said as Oliver narrowed his eyes.

"I'm sorry, who are you? And why did you break into my house?" Oliver demanded.

"Nick Fury. I'm sure Amanda Waller and Lyla Michaels have mentioned me," Fury said as he got to his feet.

"Yeah, Waller was always in a mood whenever she got out of a meeting with you. Takes a lot to piss her off, good job," Oliver said and Fury's lips twitched like he was fighting a smirk. "Thought you were dead."

"Could say the same about you," Fury pointed out and Oliver nodded.

"Fair enough. What are you doing here?" Oliver inquired.

"Prometheus," Fury said and Oliver tensed.

"What do you know about him?" Oliver demanded.

"A lot more than you. I've been tracking him since he first showed up. He's managed to find out almost every detail about your life, managed to turn a member of your team against you. He got in your head, been one step ahead of you this whole time. But to be one step ahead of me, he needs to keep both eyes open."

Fury removed his glasses and Oliver almost started at the scar on Fury's eye.

"Adrian Chase," Fury said and Oliver stared at him. "He is Prometheus."

Oliver stared, the words sinking in. As he digested it, little things started making sense. Adrian's passive aggressive comments towards Oliver when they first met. How he knew about Malone, the exact details before anyone else. How he was the one to tell Oliver about Malone being abducted. It all fit.

City Hall, next day

Morning

Oliver was staring out the window of his office the next day when there was a knock on the door.

"You asked to see me Mr. Mayor?" Adrian asked as he stood in the door.

"Come in, close the door," Oliver ordered, turning around as Adrian complied.

"Is there a problem?" Adrian asked innocently as he reached Oliver's desk and Oliver smiled tightly.

"You think you're so smart," Oliver said as he pulled out a letter opener, swirling it. "You think you have me all figured out. But if you had…you really would have seen this coming."

Oliver then placed a hand on his desk and, to Adrian's shock, stabbed his own hand with the letter opener. Oliver let out a howl of pain and, moments later, Diggle and the rest of security burst in.

"He just stabbed me!" Oliver yelled, putting on a show of an attack victim as he pointed shakily at Adrian with his other hand. "He's crazy!"

Before Adrian could figure out what had happened, Diggle and the other security guards had tackled him to the ground, forced Adrian's hands behind his back. As it sunk in, Adrian laughed. Not a regular laugh, but an insane, unhinged laugh.

"Well played Oliver, well played," Adrian said an insane glint in his eyes.

Argus base

Night

"We ran the DNA test, Adrian Chase is the biological son of Justin Clayborne," Lyla said as she met Oliver, his hand wrapped from where he had been stabbed, in her office.

"So Fury was right," Oliver muttered and Lyla nodded.

"We've come into contact a few times, he usually is," Lyla said as she got to her feet. "Chase is going to be transferred to Lian Yu in the morning; he's under constant guard at the moment. He's not going to be a problem anymore Oliver."

"Good," Oliver said in relief.

Suddenly, his phone started ringing. Pulling it out, Oliver saw it was an unknown number. Frowning, Oliver answered it.

"Hello?" he said wearily.

"Nice job," Fury said.

"Only thanks to you. I never said thanks," Oliver said.

"And you'll never have to. Just remember, keep both eyes open Queen," Fury said before hanging up.

Chase, to be blunt, was a poor villain because the plot is written to accommodate him. The main characters are written as practically being brain dead not to figure out Chase is Prometheus when, in hindsight, there are numerous things that should have raised a red flag. The fact that Chase was the one who alerted Oliver to both Billy being captured and his death, with full knowledge of the exact circumstances when only Oliver, Team Arrow, and Prometheus would know that was a huge give away looking back.