Castiel was laying at Dean's side one night, almost asleep, when he felt an uneasy sensation in the pit of his stomach. It felt like they were being watched. He looked up, glancing around the room uncomfortably. Dean scratched him behind the ears, telling him to calm down as he changed the channel.
"Cas, relax," Dean said, noticing Castiel still wasn't calming down, "What's got you so nervous? It's calm and quiet out."
"Well, well, well... Hello, Dean," said a cold voice.
Dean looked up to see Lucifer standing near the door. Castiel snarled, low, long, and loud, his hair standing on end. He knew this had to be Lucifer, who still technically was his brother, but had betrayed their father.
"Oh, you have a guard dog now? How pathetic of an attempt to protect yourself," Lucifer sneered, looking at Castiel.
Castiel's snarl grew louder as Lucifer approached him and Dean, standing to protect the human he cared for so much.
"Bad doggie!" Lucifer said.
Castiel's collar started to tighten around his neck, cutting off his oxygen supply and making him choke and gag.
"Leave him alone!" Dean yelled, standing, "What do you want, you damn bastard!?"
"I want you to convince your brother, who doesn't seem to be here at the moment which is unusual... To hand himself over to me already. I need him to be my vessel," Lucifer shrugged, looking around the hotel room.
He let Castiel breath again, smirking.
"No," Dean said.
"Excuse me?" questioned Lucifer.
"I said, no," Dean snarled.
"Do it or the dog dies," Lucifer warned.
Dean looked at Castiel who was still trying to get his breath back, panting and gulping down as much air as he could.
"...You bastard," Dean growled.
"Make your choice," Lucifer said.
Castiel lunged at Lucifer, sinking his sharp canine teeth into his vessels hand. Lucifer snarled and shook him off.
"Mutt," he mumbled.
Castiel shook off, getting up. He ow went for Lucifer's neck, biting hard but barely harming him because Lucifer healed in a flash.
"Cas, he'll kill you!" Dean said.
"Cas? Castiel?" Lucifer asked.
Dean was silent.
"That is too rich!" laughed Lucifer, picking up Castiel by his scruff.
Castiel snarled, trying to bite his brother.
"Bad boy, Castiel," Lucifer said.
With that he threw Castiel across the room and into the wall, knocking him unconscious. Dean's eyes widened at the sight of his angel and he scrambled to get up and help him, not wanting him to get hurt because of him.
"Don't. Move," Lucifer warned.
Dean heard a growling but couldn't see the source. Hell Hounds.
"If you move an inch, my own pets will attack your precious little Castiel and send him back where he belongs," Lucifer said.
"...I won't give up Sam or Castiel, you bastard," Dean growled.
Lucifer smirked and bowed, "Thank you, thank you very much."
Dean wasn't sure what his next move should be. He noticed Castiel behind Lucifer, struggling to get up, once more awake. He wished he could tell Castiel to stay down, to let him fight this one alone so Castiel wouldn't be harmed further, but didn't want to risk Lucifer sending the Hell Hounds on him and killing him.
"...What if I say I'll be your vessel?" asked Dean.
"You? Why you?" questioned Lucifer, sitting on the bed, crossing his legs, "Take a seat. Let's act like civilized gentlemen."
Dean sat on the other side of the bed, casting a wary eye at Castiel before looking at Lucifer. Castiel had flopped back down, panting hard, pain written on his face.
"I'll let you use me as your vessel as long as you don't harm Castiel or Sam. They mean too much to me..." Dean said, voice shaking slightly no matter how hard he tried to sound calm, "Do we have a deal or not?"
Lucifer smirked, "You sir, have just made yourself a deal with the devil."
Dean and Lucifer both extended their hands, about to shake on it to make it official. Castiel knew he couldn't allow it to happen. He forced himself up, whining in pain softly. Ignoring the pain that was affecting his whole body, Castiel jumped up, jumping between them and forcing them apart, snarling at Lucifer.
"I warned you, Castiel," Lucifer snarled.
A new pain shot through Castiel's back right leg and he saw blood pouring from, yelping in pain as the Hell Hound bit.
"Stop!" Dean shouted.
"Our deal is off," Lucifer said, watching as the invisible dogs began to attack Castiel.
Barks, snarls, yelps, and whines filled the air as Dean tried to grab Castiel and pull him out of the fight. Deep, blood drawing, teeth marks covered his wrist when he tried to scoop up his angel and he yowled in pain, yanking his hand back. Castiel made heartbreaking yelps of pain, wishing Dean could help him, as the invisible mutts attacked him, drawing blood and breaking several of his bones. But at least Dean was safe. Except for the bite.
"Just leave us alone!" Dean yelled.
"No, you both need to be taught a lesson," Lucifer said.
He kept watching as his Hell Hounds tried to kill his brother, drawing blood from his body and on a few occasions breaking bones.
And then he was gone.
Castiel collapsed, never having felt so much pain. He didn't know why he couldn't heal like this and was sure he was going to die.
"Cas..." Dean whispered.
Castiel whined, wishing the pain would stop.
"Cas?" Dean repeated, bending down.
Castiel whimpered this time, not wanting to move an inch the pain was so bad. But Dean was safe and alive.
"Cas, I need to get you help..." Dean whispered, "I'm sorry, but this will hurt... It's the only way though buddy..."
He picked up Castiel as carefully as possible and carried him to the Impala. Castiel whimpered, feeling the pain worsen. Dean felt his heart break at the sound and got in the drivers seat, driving as carefully but as quickly as possible to a 24/7 emergency vet he'd seen when they had been going to the hotel and pulled into a spot.
After almost two hours of waiting, the vet came out.
"Are you Castiel's owner?" she asked, approaching Dean.
Dean nodded, "I am. Is he okay? Is he alive!?"
"Yes, he's alive. Castiel has three broken ribs, his back right leg is broken, his front left leg is broken, and he had to get close to a hundred stitches. Now... What did you say happened to him again? We need to have the information on file," she said.
"I was taking him for a walk and there was a pack of strays that attacked me first. That's how I got this bite on my arm. Castiel tried to defend me from them but the dogs did a number on him in the end. I finally scared them away but he was already so injured. This is all my fault... I couldn't protect him... I feel so bad... I'm a horrible pet owner..." Dean said, looking down at the blue and green tiled floor, trying to hide the tears that were gathering in the corners of his eyes when he remembered the sounds of pain and fear he'd heard.
"It's not your fault, Mr. Winchester. Accidents do happen. But we'll get him back on his feet as soon as we can," the vet said, feeling bad for Dean, "Trust me, I hate seeing an animal in pain. That's why I have this job. To help injured animals feel better. Castiel will heal with time. You need to trust me on that, okay?"
"Okay... What can we do for him...?" Dean asked.
"Well, we've got him in casts for now, along with his stitches. He also has a cone to keep from going at the stitches and casts. He'll need plenty of rest, along with some prescription pain killers and antibiotics. We're going to keep him over night to be safe. You can get him in the morning," the vet said, smiling kindly.
Dean nodded and sighed, "Thank you... Can I come in any time in the morning or should it be a certain time?"
"Around 11 a.m. should be fine. Then you'll need to fill out some more paper work and pick up his prescriptions," the vet said.
Dean left slowly, wishing he could have helped his angel further and protected him further but it was too late. He got back to the hotel and saw Sam still wasn't back so he sent him a text, letting him know what happened and asking where he was. He soon got a text back saying he'd be back at the hotel in the morning and that he'd scored at the bar. Dean smiled a little, proud of his little brother and got in bed, missing the feeling of Castiel's soft, warm, furry body pressed against his as they both slept.