Sadie Dean lives in Boston, Massachusetts, near the Carew family residence during the narrative's Boston segment. She is a wealthy child possessing vibrant orange hair cut to neck length and striking purple eyes. A defining feature of her attire is a straw hat adorned with a ribbon on top and secured under her chin with ribbons.

Sadie initially presents a snobbish and judgmental attitude. Upon encountering the protagonist shortly after the protagonist's arrival in Boston, Sadie perceives her disheveled post-journey appearance and immediately accuses her of being a thief. This establishes Sadie as an early antagonistic figure.

Sadie's demeanor undergoes a significant transformation. Her initial hostility towards the protagonist transforms into genuine friendship. She becomes actively interested in the protagonist's personal relationships, strongly supporting a developing romance between the protagonist and her childhood friend. Sadie also champions a romantic connection between an older, wealthy bachelor and a wealthy dowager within their circle, positioning herself as an enthusiastic advocate for these pairings.