The Netflix plot summary states that season three will show the aftermath of the falling out between Penelope and Colin's sister, Eloise (Claudia Jessie).

At the end of season two, Eloise discovers that her best friend Penelope is Lady Whistledown. This comes after Penelope publicly disgraces Eloise in one of her Whistledown newspapers to save herself from Queen Charlotte's (Golda Rosheuvel) wrath. 

"Complicating matters for Penelope is her rift with Eloise (Claudia Jessie), who has found a new friend in a very unlikely place, while Penelope's growing presence in the ton makes it all the more difficult to keep her Lady Whistledown alter ego a secret," the Netflix summary reads.

The trailer implies that Eloise's friend is the show's notorious bully, Cressida Cowper (Jessica Madsen).

During a press conference on February 14, Jessie said that Eloise will be embracing societal traditions since she no longer can count on her friendship with Penelope. Jessie and Newton also said that Eloise will be overprotective of Colin as he pursues Penelope.

"Ultimate third wheel," Eloise said.

Brownell told Variety in May 2022 that Colin's older brother, Benedict (Luke Thompson), will be a "vital part of season three." This may mean season three will sow the seeds for a romance involving him.

During the press conference, Thompson said Benedict is still struggling to find his path, but he is "taking on the responsibilities" of his older brother Anthony.

"He can step into quite a few different roles and happily do that but there's always this question at the center which is 'Who's he? And what does he want? And where does he fit in?'" Thompson said.

Brownell also confirmed that the series will not include Penelope's weight loss story from the books.

"We think that Penelope is beautiful, and I don't think it's really a part of her story," Brownell said.