Dean was shuddering ceaselessly when they returned. His head was once again bowed, as though he was trying to curl in on himself. The chain of the collar was pulled taut, clinking faintly in time to his shivers.

Cas went first, as usual. Dean cringed away from the needle to his neck like a trapped animal avoiding a hot poker. His snarls became cries of torment, and though his chest heaved with the force of each breath, his head did not lift.

Sam pricked the crook of his arm for a sixth time. He looked like a junkie with all these track marks. Dean merely flinched when the needle pierced his forearm, pulling any slack out of the chain as he curled forward, shaking violently and wheezing with each heaving breath.

"Sa-am ..."

The choked whisper was so faint, so broken, for a moment Sam couldn't believe it had come from his brother. "I'm here, Dean. I'm here."

He put a hand on Dean's shoulder and squeezed, feeling the very bones tremble.

"Sa-am ... plea-ease ..."

Sam looked up at the ceiling, blinking quickly. He rubbed his brother's back in small circles, but said nothing.

"Sam ... i' burns ... pleas –" A fit of fierce coughing consumed the rest of his words and Sam's hand tightened over the shivering shoulder.

Once the coughing had been replaced by deep, wheezing breaths, Sam took a few steps back and returned to his chair, casting a desperate look at Cas, whose eyes looked at tortured as Sam felt.

Silence fell, but for Dean's laboured breathing. After thirty-seven anxious minutes, Dean's shudders finally subsided. His head raised minutely, his shadowed eyes searching.

They settled on Sam.

"You're ... you're selfish ... y'know that?" Dean panted, staring at Sam from under his sweat-drenched brow.

Sam didn't rise to the bait. "Save your energy, Dean."

Dean ignored him. "I was ... happy. For the first time in my life. And now ... rather 'an let me be, you – you're killing me. So you won't be alone. Or g-guilty." He spat a globule of bloody saliva onto the floor. "Pathetic."

Sam shook his head, smiling. "I know you don't mean that. You may as well save your breath, Dean. I'm not gonna stop."

"Y-your gonna cure me?"

"That's right."

"'Cause, what, I'm ... diseased?"

"Yep."

"And what if I like the disease?" he hissed, leaning as far forward as the chain would allow.

Sam exchanged a glance with Cas. "That doesn't matter. You like being human more."

Dean's laughter boomed through the dungeon, but was quickly suffocated by hacking coughing. "You think that? Really?"

"I know it."

"How do you like being human, Sam? How do y-you like seeing Kevin die ev-every night? How d'you like counting corpses when you try to sleep? How d'you like waking up in the m... the middle of the night from nightmares of Hell and ... all the p-people y-you hurt ... killed ... huh?"

Sam clenched his teeth. "It's worth it."

Dean snorted. "Ha! Worth what? What exactly makes up f-for all that pain, Sam?"

"My brother."

Dean smiled in disbelief, spitting another mouthful of blood onto the concrete.

"My brother makes up for it. And Cas," he said, gesturing to the angel. "And Garth, and Charlie, and Jodie, and Kevin and Bobby – all the friends I've made –"

"Who're dead," Dean spat.

"All the friends who have fought with me," Sam continued, raising his voice to drown out the demon's. "And all the lives I save. All the people who're alive because of me. And yeah," he added, knowing what Dean was about to snarl. "A lot of people have died because of me, too. And that haunts me, it does. But I still try. I still fight. I make a difference. I know my purpose. And I know that someone's always got my back.

"That's why it's all worth it."

Cas stepped forward to stand at his side, smiling proudly up at him.

Dean let out a long-suffering groan. "What a load of bull." He tried to straighten his back but didn't seem able to uncurl himself fully. "As if that makes up for being a monster."

"Monster?" Cas scoffed. "That's rich coming from you, demon."

Dean chuckled darkly. "First of all, look who's talking, Mr. Almighty. Second, I'm just being true to who I am, doing what I do and doin' it well. Sam, on the other hand." He swiveled his head to glare at him. "You claim to be some great savior, that the means justify the ends. Well, what were those means, huh, Sam? How many people did you torture to death, not even caring whether or not they were a demon? How many people did you trick into helping you, no matter what it cost them, hm?"

Dean slumped in the chair, the chains clanking. He glared at Sam, panting as he recovered from the effort of his accusations.

"I heard what you did, Sam. You re... you really think your dear brother will be able t-to forgive you for all that?"

"Yeah. He will."

Sam's watch sounded for the seventh time. Without looking away from Dean, Sam picked up a syringe as Cas readied his own. "In just about an hour, I think."

Dean's mask of bravado cracked as Cas stepped forward with the filled syringe. His breathing quickened and his gaze turned pleading.

"For god's sake, just kill me already! Stab me, cut my throat, why drag it out!"

The sincerity Sam heard in the words made his stomach shiver with unease. Cas hesitated too, but for only a moment. He injected Dean in the neck, stepping back quickly as Dean was wracked by a new, violent seizure. Sam had to hold his bound arm to keep it still enough to add his half of the treatment. Once the plunger had forced the last drops of confessed blood into Dean's veins, his head jerked back, his black eyes opened and he screamed.

Sam had never heard his brother make a sound like that. It was beyond mere pain. It surpassed fear. It bounced off the hard concrete walls and pierced Sam to his very core. It didn't even sound human. No living man or woman could ever produce a screech so chilling, so utterly consumed with agony and live to hear its echo. Sam doubted an animal could produce such a scream either.

And yet, Sam recognised the sound. The darkest parts of his soul remembered it. He had made that sound in the Pit, when Lucifer had punished him. It was a scream beyond the skill of Hell.

It was the sound of a soul breaking apart.

Even when his voice broke and his lungs were emptied, Dean's posture remained unnaturally rigid, his mouth stretched wide in silent anguish. Finally, thankfully, with a slight shiver Dean passed out.