Nan is a young orphaned girl who is initially raised by a mysterious and magical chimney sweep known to Nan as simply “the Sweep.” The Sweep mysteriously disappears when Nan is six, and she then becomes an indentured worker for the cruel Wilkie Crudd, owner of the chimney sweeping business The Clean Sweep. She is a capable and skilled chimney sweep because the Sweep has long since taught her all the tricks of the trade.

Nan is a dynamic character who changes greatly throughout the course of the novel. She is terse with the other children she works with, except for a soft spot she holds for Newt, a new boy who cries himself to sleep each night. She is especially acerbic to Toby, a young boy whom she has known all her life, and who always greets her affectionately as “Smudge.” Nan’s naturally kind nature is reawakened by Charlie, a protective golem made of soot who saves her life in a chimney fire. Nan and Charlie make a home together in an abandoned mansion that they call the “captain’s house.” Toby regularly visits, and the three become family to one another, along with Toby’s rat, Prospero, and Charlie’s beloved bird, Dent.