"Looks like you are well and truly on your own."
Crowley's last words echo in the empty lab long after he is gone. Sam looks around. Damaged equipment, splatter on the walls, emptiness that yawns. He is scared, and screwed. He should've held onto Dean; should've watched over him when he went for the kill. He should've been there right next to him, next to Cas, held onto them so neither would get blown away by the blast. That bone had been an unknown element; such things always came with a fine print in the manual. They should've predicted it. Dean should not have done it alone. Sam and Dean. Always as one. Only Dean had asked him to rescue Kevin and he'd gotten to the lab late. It had been sloppy on all fronts and all it did was giving Crowley his absolute victory.
Crowley was the only one left. Dean was gone. Bobby was gone. Meg was nowhere to be found. And Cas…Cas was gone too, taking with him the only ally he could count on to save Dean. Sam would have to do it all by himself, with no clues where to start.
He looks at the spot where Kevin had disappeared, at the leviathan corpses scattered around. He should probably start with the bodies; do something with the heads so they won't get reattached. He should keep the remaining leviathans from reorganizing like Crowley had suggested, stop the delivery of the poisoned food, warn people, kill the rest of the bad guys. He should find those who have been infected and help them. Find Dean. Find Cas. Save Dean with help from Cas. Save Dean so they could do everything together. He should not do anything before saving Dean first.
Sam's breath starts speeding up. There are dots in his vision and he can't tell them from the splashed leviathan goo on the walls. The air around him is thick with fumes from dead flesh and strong chemicals. This place is hostile, scarier now than when it was swarming with monsters. Loneliness is a suffocating swell and Sam feels its volume more than ever now.
He turns to look at the door, looks at the corpses again. He should clean them up, separate the heads from the bodies, stop the shipment of the creamers, find Kevin's mom, warn people about the food, find Crowley, find Meg…he needs to get out of here.
Something clicks. He looks up. It's the clock. He's already late. He hears movement in the halls. Demons or Levis, it doesn't matter. He realizes he is frozen, can't bring himself to leave the spot where Dean has disappeared. Not that he's hoping Dean would come back magically. He simply doesn't know where to go. If Cas were here he would tell him. If Bobby were here he would scout the area for clues. If Meg were here she would fight the enemy until Sam figured out what to do.
If Kevin were here he'd probably dragged him out already.
But nobody is here. He is the only one left and he's useless and helpless and alone. He can't move his body, can't draw in breath, can't walk, or hide from the enemy marching outside. All he can do is stand and repeat the image of Dean and Cas disappearing in his head and wait for the monsters to arrive.