A/N: This started as a drabble, but my muse blew it up to a multichap. Speculation fic, based on spoilers through 3x20.
Time and reality ceased to exist in his mind. The drafty air swirling from the high, stone ceilings brushed unnoticed past his cheek. The pops of firelight and the murmurs of everyone behind him fell on deaf ears. The flickering light reflecting off the dark water fell away to the only thing occupying his vision: the unnaturally still body of Felicity Smoak.
Her skin was too pale. He had always admired her pearlescent complexion, with her perfectly painted lips and flawless eyes, but he never realized how colorful her skin was—until it wasn't. Her hair, which he secretly thought had its own personality, was laying lifeless against her head in a wet, tangled mess. The hand that was always soft, always warm, was currently lying cold and limp in his tight grip.
His knees were screaming at him after hours of kneeling on stone, but that pain was drowned out by the one in his sternum. The only thing that seemed to relieve the pressure was talking to her, pleading with her. As words fell from his lips and tears fell from his eyes, the tightness in his chest loosened, bit by bit.
"Please, Felicity, open your eyes," he whispered, his voice cracking from overuse. "I can't do this without you. Come back to me. Please."
He swayed gently from side to side as he spoke, praying to whichever deity would listen, even though it was a practice he abandoned after nursery school. He was assured it was unnecessary, as the water would do all the work, but he couldn't ignore the compulsion that was born out of his despair. Living in a world where Felicity didn't exist was unacceptable. There was nothing he wouldn't do for her, no lengths he wouldn't go to, nothing that would stop him from having her in his life.
"Felicity," he croaked, "I need you. Don't leave me, please…" He squeezed her hand, desperate to feel some kind of response. A tightening on his hand. A fluttering of her eyelids. Anything—
She gasped loudly as her body surged upward, her eyes and mouth popping wide open. Oliver jerked forward in his haste and almost fell into the pool.
"Felicity!" he shouted, diving his free hand under the water to cradle her neck. He helped her to a sitting position as she continued gasping and coughing, trying to get more oxygen into her lungs. A clamor of footsteps pierced his awareness, and to his protesting outrage, strong arms wrenched him away from Felicity, while other arms took his place around her body.
"Let go of me," he growled. He did not travel all this way, and wait all this time to be separated from her when she finally came back. He turned to his captor behind him and got close to his face. "Let go!"
"Let him go," came the soft, booming voice of Ra's Al Ghul, and he was finally released. He ran back to Felicity's side without a second thought, who was currently being helped out of the pool and wrapped up in a plush, velvet robe.
"Felicity?" He stopped in front of her and cupped her face, lifting it to look into her eyes. He wasn't prepared for what he found.
She stared through him, a vacant, crazed expression in her eyes. A cold feeling settled into his gut, and he repeated her name softly, trying to reach her. There was a split second of something that resembled lucidity, where she looked directly into him in a panic, and that was his only bit of peace before all hell broke loose.
She opened her mouth in a primal scream before breaking away from her handlers, raising her hands to scratch and claw at Oliver's face and chest. His body's instinctual defenses deflected all of her attempts to hurt him, but his mind felt disconnected from his actions, staring at her with horror.
She was wrangled into submission by two of the League members, who whisked her out of the room and away from Oliver. He stared after her departing form in shock, and the terrifying blankness in her eyes lingered in his mind, sure to plague his dreams tonight.
Ra's Al Ghul walked into his line of sight, and Oliver's eyes crawled up from his boots to meet his gaze. "The waters have an unfortunate side effect on the recently deceased," Ra's explained. "Fortunately, however, the side effects are temporary, and she should be restored to full health within a few days. Now," he said, stretching out his hand to help Oliver to his feet. "I believe we have an accord?"
Oliver hesitated before accepting his hand. He knew what taking it meant. And he knew, ultimately, it was worth it. Saving Felicity was worth all the pain and darkness in the world. He only hoped she would forgive him.
He reached up his hand to accept his enemy's, and got back up on his feet. "We do," he replied, and thus began his apprenticeship in the League of Assassins.