Death of her Girlfriend
Caitlin is setting up candles and lanterns in a tent while talking to her girlfriend. The two begin to kiss. Emily notices a huge bug, and her girlfriend slaps it away. Suddenly the entire tent is covered in bugs and Emily, runs out of the tent screaming. She’s followed by her girlfriend, but Emily has disappeared so the girl runs back. Back at the tent, Caitlin is approached by Cora, but then Isaac appears and attacks Cora. Scott and Derek appear as backup, and Cora runs, with Derek and Isaac right behind her. Scott stops to ask Caitlin if she’s okay and tells her to get out of the woods as quickly as possible. Later, The Sheriff and one of his deputies are discussing what happened to Caitlin. She tells the police she saw a girl with glowing eyes and fangs, but she admits that she and her girlfriend had split a tab of MDMA, which is a known hallucinogen. At the hospital, Sitles and Melissa go talk to Caitlin. With Caitlin’s help, Stiles puts together that she wanted it to be a romantic evening, wanted things to be special for Emily’s first time. 
Caitlin goes to the party at Derek's loft where she sees Stiles. Caitlin comes up and kisses Stiles on the cheek, and he decides to stay. He follows Caitlin into the crowd. Stiles catches up with Caitlin. She doesn't recognize him from when they met before in the hospital. Stiles asks her how she's doing with the fact that her girlfriend died. She says that she's okay and really drunk and then asks him if he wants to dance. Caitlin brings Stiles a beer and asks if he has a bottle opener. She takes his keys from his hand and points out that his key as phosphors on it. They both look at the key closely, and then Caitlin leans up and kisses him. Stiles is surprised because he thought she liked girls. "I do like girls. Do you?" "Absolutely." "Great." "So you also like boys?" "Absolutely. Do you?" Stiles doesn't answer her, but he gets an expression on his face that looks like revelation. Caitlin smiles and kisses him again. Stiles breaks off the kiss to ask her what phosphors are. She explains that they are a substance that luminesces. They're found in laundry detergent and in the paint they're wearing. They kiss again, but Stiles stops suddenly. He asks how he'd get phosphors on his key, and she asks if he's been handling chemicals. Stiles suddenly realizes that he knows where there are chemicals. He gets up, apologizing profusely. He runs away, then comes back and gives her a bottle of water telling her to drink the whole thing, then leaves again.