The body has lain there four months before any use is found for it again. The darkness below ground has hidden the macabre effects of time: dead skin; putrefied and decaying. Empty eye sockets and hollow cheeks where tissue and muscle have atrophied. Bones protrude from beneath their thin and ruptured cover, displayed where shredded flesh left them exposed. Dried vessels where blood no longer flows beneath a papery veil, stretched taut over a brittle skeleton to hold in rotten organs. Gaping synapses that are no longer bridged by the electric commands of thought and feeling.
A broken shell for a broken soul that's about to be forced back in.
The corpse lies in the dark, but no light is needed by which the angel will work. His hands come to rest on the cadaver as life flows from his grace back into the body beneath him. Fluids rush and cells replicate, revived. Ligaments and sinew knit back together. Neurons fire across pathways that have been long deserted. Muscles twitch and a roaring thump resounds in the silence as a dead heart flutters back to life. Stale, cold air is sucked into lungs screaming for their first taste of oxygen in months.
Still no light reaches eyes that flicker open, but it's only a matter of time.
As Dean gasps and awakens, his memories of Hell not having yet had time to etch themselves into his newly remade brain, Castiel slowly draws his hand away, disconnecting both from the hunter's body and soul. The mark of his grace lingers, burned into skin where he gripped on tight, but despite this blemish he knows he's done well.
Dean Winchester has been restored, just as he needs to be, and Castiel smiles as he looks down at his work.
A hand begins to reach towards the daylight, and far below the towers of Heaven, an angel watches as a dead man back from Hell crawls out of the earth.