Elena Lindt is as quiet and reliable as her older sibling Dora is vivacious and unpredictable. The sisters have always been best friends who tell each other everything, yet when Dora's behavior becomes erratic and she is hospitalized with depression, Elena is stunned. She had not recognized the warning signs, and is completely at a loss as to why her sister's illness came about, and how she should respond to it. During one of Dora's periods of lucidity, she asks Elena to "save" her, and Elena, being the loyal and dependable sister that she is, determines to do just that.

When Dora returns home from the psychiatric hospital, she is a different person from whom she used to be. Dora ditches school and surreptitiously refuses to comply with the medicinal regimen prescribed by the doctors, lying to her parents and hoarding her pills. Elena tries to cover up for her sister both at home and at school, but finds that despite her best efforts, she cannot do enough to make a difference. In the wake of Dora's difficulties, the entire Lindt family begins to fall apart. Elena's parents send her to a therapist, but beyond that, they are unresponsive toward her needs in their single-minded desperation to find a cure for Dora. Overcome with confusion and guilt that she does not know how to help her sister, Elena is struggling to cope on her own when she is befriended by a quirky neighbor boy, Jimmy Zenk, who seems to know a lot about dealing with situations like Dora's. Elena continues to persist in her efforts to be a caretaker for her sister, despite the gentle admonishments of both Jimmy and her therapist that the task she has set for herself is impossible. Ultimately, when Elena reaches her own breaking point and is forced to accept the fact that she cannot save Dora, Jimmy is there beside her, a trusted friend who lends his support. No one can make Dora better unless Dora is willing to help herself, and when Elena realizes this, she is finally able, with Jimmy's help, to lay down her heavy burden of responsibility.

Published in 2008, Black Box is notable in the genre of novels about mental illness in that it focuses not on the victim of the disorder herself, but on her family. The effect that depression has on loved ones is devastating, and the author, Julie Schumacher, explores this situation with unflinching honesty. The book is fiction, yet the shame and isolation suffered by victims of depression and those who love them is realistically portrayed with deep sensitivity and understanding. The author fulfills in an unqualified manner her stated purpose of providing a vehicle through which those who have experienced any part of the trauma of depression might find comfort in the realization that they do not suffer alone.