There are many types of mysteries, but one stands out over all the others: the ones involving a Locked Room. Over the years, every mystery writer worth his salt has tried to come up with the one that tops all the rest: the secret compartments, doors locked from the inside, confused timelines, etc. It's all been tried over and over. Jacques Futrelle set the standard with his Problem in Cell 13, and John Dickson Carr raised it a bit in his The Hollow Man, and Gene Grossman throws his hat into the ring - not with a mystery taking place in a locked-room, but with a murder that takes place in a room with a completely open-door - but also with an invisible murderer. As an extra bonus feature, after this last Peter Sharp Legal Adventure, the entire text of Jacques Futrelle's Problem in Cell 13 is set forth for your reading enjoyment.