🎶Carry on my wayward son, there'll be peace when you are done. Lay your weary head to rest, don't you cry no more.🎶
When we last left off, Castiel devoured all the souls in Purgatory. He proclaimed himself God and he was a vengeful God.
"I'm you're new God," Castiel said, coldly. "A better one; so you will bow down and profess your love unto me, your Lord... or I shall destroy you."
All the Purgatory souls were too much for poor Castiel, though, and he had to put them back. All the monstrous souls went back to Purgatory except one: Leviathan. Cas ran to the outside river and submerged himself, never coming back up. Unfortunately, the Leviathan were not destroyed by Castiel's hunt for Red October. They were suddenly everywhere. Coming out of the drinking fountains, garden hoses, the kitchen sinks. The Leviathan were here to stay.
Sam and Dean were lost. They no longer had their guardian angel watching over them. Dean was especially hurt; we all know they have an epic bromance. Leviathan are older than anything, there is no lore on them and Bobby doesn't know anything if it's not in any books.
As it turns out, the Leviathan can take the form of any human with one touch. The leader of the Leviathan takes the form of Dick Roman, a political mover and shaker. It's obvious he's up to something shady. A couple of Leviathan, lower on the totem pole, take the forms of Sam and Dean. The Not Sam and Not Dean commit a string of murders, putting Real Sam and Real Dean in the police spotlight once more. They ditch the Impala. ::tears!:: Bobby, having captured a Leviathan, discovered a way to hurt them: Borax. It doesn't kill them, but it slows them down enough to have their heads lopped off. By keeping the body and the head separate, they can't come back to life.
Armed with machetes and cleaning solution, Sam, Dean, and Bobby head for the office building of Dick Roman, intending to find out what that mother is up to. During the getaway, Dick shoots Bobby in the head. Many tears fall during the episode 10 of the season, "Death's Door." Bobby spends the episode in a coma, trying to fight death. Sadly, not even Bobby can run from the inevitable. His final word will sit with me forever: "Idjits."
From then on, the boys are wracked with grief (who isn't?) and spend their time drinking beers and feeling sad. Things happen that makes us think 'Hey, that's weird. Maybe Bobby is a ghost!' It goes back and forth, is he, isn't he, we just don't know. Well, it turns out he is! BUT Sam and Dean can't see him. He isn't powerful enough yet.
Sam's broken mind is starting to fall apart. He's seeing Lucifer and his hand trick isn't working. Poor Sam goes days without sleeping and ends up in an institution. Lucifer will not shut up. He's talking, he's singing, he's throwing firecrackers at Sam. Dean scours Bobby's address book for anyone with information on how to help Sam. No one wants to help, until the address book falls off the table and out flies a business card. Bobby? Is that you? The guy has a name and address of one Emanuel. He claims this Emanuel is a healer, and not like the kind of healer from season 1, episode 'Faith'. The real deal. Dean tracks him down. Oh my God! Emanuel is Castiel! He's alive! He has no memory, but he's alive! Meg shows up and tells Castiel who he is, Castiel remembers, kills a bunch of demons and saves Sam. The only problem is that Castiel had to take on Sam's crazy to save him. Sam's okay, but now Castiel is institutionalized.