Content Warning: The source text references multiple deaths by suicide and deals with the psychological effects of trauma, loss, and grief. It also uses stigmatizing and potentially offensive language to refer to people experiencing mental illness.

Twenty-five-year-old Jules Larsen is the protagonist and first-person narrator of Lock Every Door. She is a dynamic character, changing over the course of the narrative. Because she is the first-person narrator, her perspective dictates the narrative depiction, atmosphere, and central conflicts throughout. Jules has been her own since her older sister Jane disappeared and her parents died. Jules’s character arc is defined by the Psychological Effects of Isolation and Loneliness, which she overcomes over the novel through resilience and pluck. At the beginning of the book, Jules struggles to support herself and build a life after being laid off from her job and discovering her boyfriend cheating on her.

Jules makes risky decisions that convey her determination to prove herself and become independent. She believes that no one else understands her situation, and therefore develops a habit of pushing others away and assuming sole responsibility for her life. For example, her refusal to accept help from her best friend, Chloe, suggests a fierce independence and desire for self-sufficiency that ultimately further isolates her.