Sam (Jared Padaleck) and Dean (Jensen Ackles) are stunned when Castiel (Misha Collins) suddenly appears back on Earth with no memory of how he escaped from Purgatory.  Meanwhile, Mrs. Tran (guest star Lauren Tom) enlists a witch (guest star Cyrina Fiallo) to concoct a demon bomb, but the witch double crosses Mrs. Tran and turns her and Kevin (guest star Osric Chau) over to Crowley (guest star Mark Sheppard).