The spell isn't solid. It's a jumbled mess of different pieces of lore Sam's stitched together. Sam knows he needs to go to sleep. He's been working on this for too long without any breaks, but he can't. He's close, and he has something that might actually work. What he's doing has never been done before, but he's willing to do it. He calls Rowena to get a second pair of eyes to look over his work, but she doesn't answer. So Sam leaves a vague message asking her to call him back.
He sets the phone down on the table and runs his hand over his face and through his hair. He's going to take a shower and perform his spell whether Rowena answers or not. He considers telling Eileen and Dean but decides against it. He doesn't want to tell Dean just in case it doesn't work; he won't get his brother's hopes up for nothing. And Eileen is going to be gone for a few days, so there's no need to tell her. He'll be there and back before she's done with her hunt. When Sam checks his phone after his shower, he's got nothing. Well, it's now or never.
The spell is a bit complex, but it's nothing Sam can't handle.
First, he'll have to gain access to the Empty. He'll have to go somewhere he knows the Empty is weak; somewhere it's released one of its inhabitants before.
The windmill creaks quietly in the afternoon sun. Sam watches it momentarily. This really is a beautiful place. He takes a deep breath before setting up his supplies. They weren't easy to bring, but Sam did it anyway. It's going to be worth it.
Next, he'll have to tame a Reaper. It's something he's seen done before; when Dean went to that faith healer years ago. Sam finds that spell easily.
"What is this?" the Reaper Sam summoned asks. He looks up at Sam in disbelief.
"You have to do what I say now, right?" Sam says.
The Reaper glares. "Death won't be too happy about this."
"Well, you're not going to tell her."
The Reaper glares at him again but doesn't say anything.
"You're going to retrieve Castiel," Sam commands.
"I can't," the Reaper informs him. "I only have access to the Empty when I'm delivering something to it."
"Let me worry about opening the Empty. You worry about getting Castiel back here safely."
Lastly, he'll have to open the Empty. This part is a little more difficult to do, but Sam figured it out by combining certain parts of Nick's failed spell (the non-failed parts, thank you very much) and the spell to open Purgatory. If Sam's work is correct, this should open a door to the Empty.
Sam pours a jar of blood onto the grass and says, "Sanguinis hoc mundo ianuam Aperio ultra. Mundus vacuus, domicilia angelorum et daemonum. Vacua mundus aperta est." while cutting into his arm, letting his blood mix with the blood already on the grass. Sam watches as his blood drips down his arm.
Any time now the Empty should be opening.
But nothing happens, and Sam and the Reaper stare at the blood-stained grass.
The Reaper laughs bitterly and looks up at Sam. "This is what you get for going off-script, kid."
Sam glares. "We destroyed the scri—"
There's a loud boom, throwing Sam backwards, making his ears ring. He hits the ground so hard it knocks the breath out of him. He's gasping for air and realizes he still can't hear. His ears are ringing, and he wildly looks around. It seems like it's later in the evening than it just was, but Sam's senses aren't completely accurate right now, so he's not really sure.
Sam stands up and nearly falls over when a wave of dizziness washes over him. He frantically brushes his hair out of his face. He forces himself to breath calmly. His hearing is finally returning, but he doesn't see anything different. Did it not work? Did his spell fail? It doesn't look like he opened the Empty at all.
Sam swallows down the lump in his throat and blinks back tears. He was so sure this was going to work. Why didn't it work? He stumbles back over to where he intended for the portal to open. He sees the faded bloodstain on the grass.
No. No, no, no! This was supposed to work! This was going to work! He was going to fix everything!
Someone groans behind him. It's probably the Reaper. Sam turns, and Castiel is lying in front of him, slowly sitting up.
"Cas!" Sam exclaims and rushes to his side. He kneels beside him. "Whoa, whoa, take it easy." Sam puts a hand on Cas' back, helping the angel sit up. Sam stares at Cas. He looks…he looks fine. He looks just like he did the last time Sam saw him.
Cas blinks. The windmill creaks, and Cas looks over at it and squints.
"Cas?" Sam asks tentatively.
Cas slowly turns to look at him. "…Sam?"
Sam lurches forward and hugs Cas. "Oh my god, Cas. I never thought I'd see you again." And Sam's crying now, but he doesn't care. He did it. He fucking did it. He brought Cas back.
"I…" Cas begins. He finally wraps his arms around the hunter. "What's happening?"
Sam sniffs and swallows. "I brought you back." Sam feels Cas immediately tense.
"Sam, what have you done?" he asks coldly.
Sam squeezes Cas tighter. "No, man, it's okay. I got you out. No strings attached."
"That…doesn't happen."
"That doesn't happen when Chuck is running things. He's out of the picture now."
They hug each other in silence for a few moments before Cas asks quietly, "So you defeated him?"
Sam finally lets go and wipes his eyes. He nods. "Yeah, uh, yeah." He stares at Cas again. He can't believe he's really back.
"You're staring at me strangely," Cas says.
Sam chuckles. "Yeah, I just… We thought you were gone, man."
"Yes." Cas squints thoughtfully. "And where is everyone?"
"Oh," Sam starts. "Uh, well, I didn't exactly tell anyone I was doing this just in case it didn't work."
"Sam," Cas chides.
Sam laughs. "I know, I know. That was stupid. But honestly? I'm just glad you're back." Sam stands up and holds a hand out for Cas to take. "I'll tell you everything on the way back to the bunker."
Cas takes his hand and stands. Cas looks around, taking in the scenery. "It is nice to be back."
As Sam leads Cas back to the car, he takes his phone out of his pocket. He taps the screen a few time and clicks the power button. "Huh, that's weird," he comments.
"What is it?" Cas asks.
"My phone is dead. Must've been the spell."