A one-shot set during Let's Kill Hitler after the voice-interface conversation.
I haven't written fanfiction in ages, but after theorizing with some people this was way too tempting.

Enjoy. ;)

The Doctor did his best not to hobble out of the TARDIS. Keeping his composure was tough when nearly every centimeter of his body felt like it was on fire. He pushed open the doors and was greeted to River sitting on her cot in Stormcage. The TARDIS did always take him where he needed to go.

"Oh, hello sweetie. To what do I owe the pleasure of this visit?"

The Doctor took a few steps and then fell against the bars to her cell. River came rushing up to him.

"What's wrong?"

"Long story," the Doctor muttered. "How are you?"

"Doctor," River said. She was genuinely worried and not about to put up with his games.

"Yes, alright! I don't have much time, River. I'll be dead in 32 minutes. Actually, probably less than that now. 30 minutes. Or maybe 29... Anyways! Let's get married."

"This isn't funny."

"I'm not being funny-" The Doctor said and then instantly doubled over in pain, clutching at his second heart as the poison shot through his body.

"You're not making any sense, Doctor. Tell me what's wrong!"

"Never mind! I don't want to marry you. No no no, don't look at me like that. Because if I do, it just finalizes that this is my end. My final act. That I only have 28 or 27 minutes left now."

"Who did this to you?" River asked, even though somewhere in the back of her mind she had an idea who did. When the Doctor looked up into her eyes and couldn't say anything, her fear was realized. She did. "Let me help you," she said quietly.

"You can't help me."

"Yes I can!" she shouted, quickly changing her tone, "I don't want to murder you!"

"There's nothing you can do!" he spat, not meaning to come off as that rude.

"Let's get married, then," River replied. "27 minutes. Let's get married."

"We don't have a priest. Or rings."

"You'd lose yours anyway."

"I don't have the proper clothes on."

"What does it matter?"

"I have a fancy tux in the TARDIS."

"Don't you dare leave- not yet," River said and a moment of silence followed. They didn't continue to bicker but just looked at each other for awhile. She didn't want this to be her last time with the Doctor, it couldn't be. She would do anything to save him, one hundred times over. She had to try.

"Doctor," she said, "I don't know exactly where you just came from, but you can't give up. You have to go back."

"No one can save me-"

"I can. Not from here, but I can. Please, Doctor. You have to find me. I don't care what you have to go and say, but you have to try."

She pulled him in for a kiss even though they were separated by the bars of her cell. It was so loving, she refused that this was going to be her last. He was going to make it. He had to. He pulled away because the pain of the poison hit him in a wave again and that pained her terribly to see. He straightened himself back out.

"Go," she said, her voice barely above a whisper.

"River-"

"Go," she repeated and the Doctor had no choice but to comply. He made his way back to the TARDIS and as he laid his hand on those blue doors he took once last look back at River. He had no idea what he was going to say, the River from the time where he was at didn't even know she was River yet. But he had to try.