Mick, with her rebellious and courageous spirit as she moves from childhood into adolescence, is the other strong focal point of the narrative—indeed, though Singer is the focus, it is arguable that Mick is the protagonist. There are more chapters devoted to Mick's point of view than to any other character in the novel, perhaps because her character is somewhat autobiographical of McCullers herself. Like Mick, McCullers had serious ambitions of becoming a concert pianist when she grew up. Mick's attachment to music is important not only as a defining character trait but also because McCullers' musical sensibility shapes the entire structure of The Heart Is a Lonely Hunter; indeed, she once referred to the book as a three-part fugue. Throughout the novel, music symbolizes Mick's energy and her pursuit of beauty; she stores it in the "inner room" of her mind, to which only she and Singer have access. Mick's plans to build a violin from scratch, for example, arise from her "inner room." Consequently, her frustration when the violin does not work is more violent than if the idea had been conceived in her "outer room"—the part of her that she allows to interact with the outside world.
Mick is the most positive and hopeful character in the novel. The fact that Mick is a child at the beginning of the novel provides McCullers the opportunity to portray the funny and poignant moments that accompany Mick's coming of age. At her worst, Mick frightens her little brother Bubber into running away after he accidentally shoots Baby in the head with a BB gun; at her best, she heroically offers to quit school so that she can work at Woolworth's to help her poverty-stricken family. At the end of the novel, Mick's final words indicate to us that her inner world remains intact and that she will continue to fight to achieve her ambitions.