Julie is the novel’s 12-year-old heroine. Since the novel is narrated from her point of view, readers get to know her through both her thoughts and actions. Key characterizes Julie as smart, resourceful, and sassy. She quickly accepts the situation when things start to go wrong and does not waste time feeling sorry for herself. On the surface, she takes action and remains calm, knowing that panicking will only make things worse. Instead of dwelling on the unknowns, she focuses on what she has learned from her dad and uses that information to guide her decisions. Julie follows safety guidelines and stays calm when things go wrong in situations like the anchor pulling and the shark attack. Acting as a foil to Julie, Mr. Jordan, arrogantly pushes safety limits and panics in intense situations. Through this contrast, Key highlights Julie’s exceptional maturity.

Julie’s character also embodies one of the novel’s themes: Resilience and Discipline. Despite the many difficulties nature brings, Julie continues to look for solutions and think through possible options. She has the discipline to listen to her dad before the dive, and to make the proper decompression stops on her ascent despite the dangerous situation in which she finds herself.