Title: Bringing The Walls Down
Fandom: Supernatural / Dr. Horrible's Sing-Along Blog
Pairing: Dean/Billy/Sam, Sam/Billy, Dean/Billy, Dean/Sam
Categories: action/adventure, AU, crossover, drama, post-apocalyptic, threesome
Length: Long (20,895 words)
Warnings: Incest, implied secondary character death

Author on LJ: entangled_now
Website: libraryofsol / entanglednow

Summary:
They had names now, the men in the 1967 Chevy Impala were Sam and Dean Winchester, and they were trying to save the world.

Review:
The first third of the story is told entirely for the point of view of Billy (aka Dr. Horrible) as he watches supernatural threats explode across the country. He tracks the attacks--ghosts, monsters, demons--and observes the attacks always end after a black Impala rolls through town.

Not wanting to be a villain anymore, and realizing that the Winchesters are being herded into a trap, Billy goes out and joins them. His entrance is pretty epic. I really loved Dean's maniacal love of the weapons Billy creates for them. There's also exploration of Billy's verging-on multiple-personality issues.

While I love this story for the action, the characterizations and overall great writing, I'm not particularly fond of incest stories; if that's a deal-breaker for you, you can read the first two chapters (which are just gen), and skip the third.

Link to the story:
Bringing The Walls Down (on AO3)
Bringing The Walls Down (on LJ) pt.1 pt.2 pt.3