Private investigator, Ed Case, is given a plain metal box to take care of after a chance encounter with a stranger on a train. The box is unremarkable apart from being highly polished and surprisingly heavy for its size. Intrigued, Ed has the box analysed and is astounded by what the analysis reveals.
However, the highly valuable contents are largely irrelevant as only the owner of the box can open it; any forced entry will destroy the contents. Ed has no choice but to take the box home and wait for the owner to collect it.
What ensues is a battle of wits. Ed must find the man who gave him the box in order to save his own life from two ruthless, rival criminals, who both want the box and the owner, to claim the priceless contents. Ed can only please one of the two and is faced with a difficult decision; who would make the most dangerous enemy?