Summer is thrilled to get an invitation to Savanna's Halloween party because Savanna is the most popular girl in school. She already has a boyfriend and looks like a teenager. After Summer accepts the invitation, Savanna starts acting nicely towards Summer. Savanna tells Summer to not wear a costume or brag to others that she got invited. Summer is so thrilled, she even feels okay about missing the Halloween parade.
Summer's happiness at being invited shows that she is actually interested in being a part of the upper crust of Beecher Prep, though her comment that Savanna "looks like a teenager" suggests that this may be because Summer is interested in appearing more grown up through association more than anything else.
When Summer knocks on Savanna's door, Savanna asks outright where Summer's boyfriend is. Summer has no idea what she's talking about until she realizes Savanna is referring to August. Savanna leads her to the basement, where Summer learns that Ximena is dating Miles, and Ellie also has a boyfriend, even though she's just as flat as Summer is. Within five minutes, Savanna and Henry tell Summer that if she stopped hanging out with August, she could be popular. They tell her that Julian likes her and offer to send him over to talk, but Summer excuses herself to the bathroom. While upstairs she calls her mom and asks to be picked up. Summer leaves the party early enough to go to the Halloween parade.
Savanna's initial comment is clearly an attempt to shame Summer for spending time with August. This is reinforced when Savanna and Henry try to tell Summer how she could be popular, though their insistence that Summer only has to do one thing is possibly not true. The romantic relationship dynamics at play at the party suggest that Summer would need to agree to date Julian and by doing so, would also need to be on board with Julian's bullying.