An enterprising young sales clerk leaves home to work in a bustling department store and becomes embroiled in a series of shoplifting mysteries. She observes missing merchandise and clashes with a meddlesome official investigator whose methods complicate the inquiry. Relying on keen observation, careful traps, and help from neighbors and friends, she follows clues through apartment-house intrigues, eccentric co-workers, and neighborhood gossip. The investigation uncovers surprising suspects, provokes rivalries and reconciliations, and culminates in the amateur sleuth's clever unmasking of the culprit, showcasing themes of resourcefulness, loyalty, and practical detection.