Severus looked up from his grading. He knew that knock. He'd always know that knock.
The door opened. She smiled slightly, stepping inside like a soft breeze and closing the door so gently that he wondered if it had ever been truly open. She then handed him a scroll, tied neatly with a red ribbon, a soft smile still on her face.
"You finally finished it," he whispered. She nodded as his fingers wrapped around the scroll. "And you're sure that it's ready this time? No more problems?"
"No more problems, Severus. We can finally be together like we always wanted to be," she whispered, moving a step forward and embracing him. Their lips met, sending fireworks off in both their bodies. They fumbled backwards. He fell atop his desk and she mounted him, wrapping her legs behind him. She felt him rise, prodding her despite all of the fabric in the way.
"I have work to do. Can you be quick?" he asked. She nodded, kissing him deeper as she cast a cleaver charm that removed their clothes, piling them neatly in the corner. She allowed him inside, riding in a perfect rhythm that made them both cum within minutes.
"I'll be waiting for you in London when this is over. Can you fulfill your part?" she asked.
"If Merlin will have it," he replied. She nodded, grabbing her clothes. She piled them into her bag, opening the door while still naked. "You'll be caught. You should-"
"I'm merely a dream, Severus. I'm sure no one will notice," she winked, disappearing into the night.
Severus felt the temperature change. He looked up from his papers, his raised arm hairs tickling him because of his rode. His room was the same, his work was still before him, and his clothes were still on him. He shook his head, eying the photograph next to his desk.
"You should really stop thinking about me while you work. It's like we go into another world, one where time doesn't exist and Death can be erased," she said softly, caressing his outline from within his frame. "You'll join me soon as planned. I'll be waiting. I always was."
Severus felt the tension around him. Soon would be his time. Until then, he could dream of her, even while awake. He could be one with her always.