An American teacher in training works at Po Sing Uk, an old school in Cheung Sha Wan, Hong Kong. On the first day of class, his student Alice Leung approached him to ask about bats and echolocation, their ability to move through darkness using sound waves to determine their position. He encourages her to research the phenomenon and report her findings, but is confused when she brings back a journal entry of instructions for acoustic calibration - Alice is actually trying to achieve echolocation herself. She begins staying afterschool to use the building as her acoustic playground, blindfolding herself and cataloguing the school's geography through each object she encounters sonically. The teacher can hardly believe it, but her journal entries are detailed with impressively precise instructions and she seems able to detect the presence of people walking floors below them in the school.

Concerned for Alice's wellbeing, the teacher brings her up casually to the principal, who informs him that she has been marred by her mother's suicide. When he approaches Alice to ask about her mother she is wildly upset - she repeats desperately, much to his bewilderment, the words "I trust you" and "believe me". The next time she reports about her echolocation experience, the teacher asks her to prove it to him. She tells him to come to her apartment building that evening, blindfolds him, and leads him to the rooftop. Both blinded, she describes their surroundings in detail, instructing him to wave at the two children in the next building over. After making him promise to keep the blindfold on, she runs to the edge and begins screaming for her mother. She insists her mother is there, in the air in front of them.