On Pretty Little Liars: Original Sin, the liars meet again for a fundraising costume party. Little do they know that tensions will build between them and other guests, ultimately leading to another horrific death. Starting with the holiday prior to Angela's (Gabriella Pizzolo)'s) death, the girls leave her behind to take all the blame for their poor advice.
The liars continue to enquire about their mothers' hidden secrets and how they might be connected to A in the previous episode. A claims that they want to "punish the guilty," and among their targets is Noa's mother. Imogen (Carly Pope) doesn't want to sell her daughter's house just yet, since the girls are preparing to pay a entry fee.
When Mouse (Malia Pyles) is revealed to be meeting with a guy named Steve (Alexander Chaplin), she agrees to dress up as long as she isn't scared, since Roberta (a missing girl who might be his daughter) didn't like scary things.
Faran (Zaria Simone) suspects that Karen (Mallory Bechtel) is still alive and pretending to be Kelly. She even convinces her dance partner to massage Kelly's foot just to verify that she didn't have a scar from the razor blade incident with Karen in Episode 1. Yet, the more Faran begins to investigate the situation, the more things go wrong for her later in the episode.
Tabby (Chandler Kinney) has decided to quit her job at the local theater after seeing Karen's promo video at the screening, but Wes (Derek Klena) encourages her to continue working there on Halloween night prior to the party. Tyler (Brian Altemus) is the guy who recorded Karen drinking at the party six months before her death. She dismisses the notion when she discovers that there isn't much evidence.
Imogen dresses up as Rosemary from Rosemary's Baby to welcome everyone in the door. However, Mouse arrives later that night after spending time with Steve, trickoring and consoling him. It's possible that Mouse was kidnapped in the past, and therefore can sympathize with Steve's personal pain. At the party, Faran becomes suspicious when Kelly meets Greg, Karen's boyfriend.
Tabby slams Tyler and Greg for being on her period and causing Tabby to beat him in the face, breaking his nose. When Tyler returns to the bathroom, A invades the bathroom and kills him in cold blood. Instead of dunking Tyler's body in the bathtub, like Davie's was, A picks up Tyler and dumps his body in the back of their van.
The fifth episode concludes with a few additional mysteries that will certainly unfold in the following weeks. We're not just instigated to learn what is going on with Mouse and how her interaction with Steve is the result of an incident that she experienced in the past, but we're also left curious to learn what transpired at the Bonfire Party to both Tabby and Imogen, as hinted in their final conversation. Is Imogen's pregnancy the result of an assault? Will they grow closer because of the horrible experience they