Even though Sally is very close to dying, she follows the psychic's advice and studies the Latin incantation religiously. Her continued nightmares about Donna coming to claim her soul only make things worse. She's falling apart but the roommates are determined to see her through.
Aidan waits impatiently for Kenny to morph into a vampire, worried all the while that he might end up like Jeff, Kat's ex-boyfriend.
Josh and Nora are feeling good about each other and their plans to get married, but Josh is also depressed about his sister finding out the truth about his true nature. When he confides in Nora she encourages him to wait on Emily to come around. Nora assures Josh that it will take Emily time to get used to the idea of real life monsters. Thankfully, Aidan takes their mind off of things by building a Jewish wedding altar in the living room. When Kat shows up, things are still feeling festive, despite the fact that Aidan left her hanging after their last romantic encounter.
Once Kat brings it up, Aidan comes clean with her… well, as much as he can, and she feels better. Looks like Aidan has a new leading lady. The timing is bad, though. Ultimately they decide to send Kat away so they can help Sally fend off whatever Donna has in store for her. Even though it's the last thing she wants to do on her wedding day, Nora urges Josh to go through Donna's door with Aidan and Sally to help Sally come back. And Nora helps out in her own way too, by helping Sally shop for new haunting clothes, given Sally's about to kick the bucket from flesh rotting. They're just in time - Sally passes away and her ghost appears, but at least she's in a cute outfit.
When the time comes, all three of the roommate go through the door to confront Donna together, armed with Sally's dead heart (Aidan bring up the point that it's a potent weapon against witches) and lots of hope. On the other side, after a brief hallucination where Josh thinks he's in the woods and Aidan thinks he's back in the 1700's, they find they're in Donna's Soup Kitchen, except it's all post-apocalyptic. Ray, the werewolf who turned Josh is waiting for them. He and Josh have a score to settle once and for all. Even tough Ray turns into a werewolf, Josh is able to defeat Ray for good by beheading him. Aidan and Sally go for Donna. They fight hard and pull out all the tricks they know, including Sally's Latin incantation, but nothing seems to have a lasting affect. Donna still eats Sally's soul. It turns out however that Sally is stronger than she thought—she overpowers Donna from the inside. Against all odds, Sally has won! The three are transported back to the brownstone, where Sally is a ghost.
True to Nora's advice, Josh's sister Emily shows up unexpectedly and forces Josh and Nora to have their wedding on the spot. Kat comes back to attend as well. As things wind down, Sally is startled to see a hint of Donna's presence in the house (via candles spring into INTENSE flame randomly), Kenny does indeed turn into an abomination of a vampire and Nora gets quite a shock when Liam the purebred werewolf confronts her and Josh on their honeymoon.
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Sally faces Donna again. Aidan deals with Kenny, who is a vampire abomination. Liam wants Josh and Nora dead. One of the roomies gets a blast from the past. Season 3, Episode 13.
Are Sally and Aidan a thing? Being Human Panel Highlight from Comic-Con 2013