As Christmas cheer blankets Hamsley Black Cross, Sherman Holmes, the ever-enthusiastic and eccentric detective, transforms his office into a festive wonderland. His practical partner, John H. Garden (and his fabulous alter ego, Joanne), struggles with Holmes's holiday zeal and a rather inconvenient Christmas party invitation from the local retailers' association.

Their festive season takes an unexpected turn when Roderick Fredericks, a jeweler's son, bursts into their office in a state of panic. He's lost a substantial collection of valuable second-hand jewels that he foolishly took home to clean, desperate to avoid his father discovering the mishap—and especially to keep it from the police.

As Holmes and Garden embark on a search that leads them from fingerprint powder mishaps to conversations with Holmes's surprisingly articulate talking car, they navigate a web of secrets, family dynamics, and a rather curious cleaning lady. Can their unique brand of detective work, perhaps aided by Joanne's newly acquired "bespangled fur" jacket, crack this curious case before the holidays are ruined and Roderick's father returns?