Bonnie visits Virginia in the hospital for more information about the Armory's vault. She learns that no one knows what, or who, may be lurking inside, but whatever it is strips those who enter of their compassion, empathy, and ability to love, eventually driving them mad. Virginia's sister was locked inside and she wants Yvette to stay there.
The guys, meanwhile, continue their vampire killing spree to keep up their end of the deal with Rayna. Damon pairs Stefan up with Matt. Caroline tags along with Alaric. On their road trip, Stefan learns why Matt has such a vendetta against him. He was happy with Penny and Matt believes Stefan is responsible for her death since so many things about her accident don't add up.
Bonnie's magic returns and she knows the Armory is close to locating her. When she can't find Enzo, she decides to inject herself with Rayna's blood. Rayna warns her that the plan will only make her more sick but Bonnie doesn't care.
Ric tries to talk to Caroline about the situation with Stefan while they're hunting, but Caroline doesn't want to listen. Nor does she have anything to say. It's clear, however, that she's upset. Bonnie, fearing death, calls Enzo and asks him to return home. Damon convinces him it's a good plan and then makes a deal with the Armory after Enzo leaves: finish off the list and he'll give them Bonnie.
Stefan denies having anything to do with Penny's death but admits to being in town on the night she died. Caroline and Ric are aided by the Armory when they try to kill a vampire and then they're taken into custody. Bonnie and Enzo learn that the Armory is involved when Rayna begins rapidly throwing names into the fire.
Matt reveals that Stefan compelled him the night Penny died and demands to know the truth. Bonnie goes back to hating Damon when she learns what he's done. Alex tells her that she has Ric and Caroline and Bonnie agrees to open the vault for them. Stefan once again uses compulsion to help Matt remember the night Penny died.
Matt is actually the reason she's dead. He shot her in the woods on accident and Stefan helped cover it up and erased Matt's memory of the night so that he wouldn't have to live with the knowledge of what he'd done. Matt still blames Stefan for her death because if he hadn't been in town, they wouldn't have been in the woods that night.
Bonnie uses magic to open the vault for Alex. When Alex enters the vault, she finds Yvette dead. Something inside the vault begins snatching Alex's men so they clear out of the room quickly only to find that Bonnie has sealed them all inside. Damon and Enzo argue over Damon's decision and Damon says he did it to save her life and also so that Bonnie would hate him instead of Enzo.
Enzo cares for Bonnie while she rests and they both await Damon and Rayna's spell to transfer Rayna's final remaining life to Bonnie. Caroline and Ric discuss their future as a couple.
Rayna and a shaman complete the spell.