"Charlie Chan, Jimmy and Birmingham are on a bus trip to San Francisco, where he's about to investigate for an insurance company the strange and gruesome deaths of a couple of newly wed young women - all 'torso killings', where the head's been cut off from the body; and now another victim has been found, and the lady who sits next to him on the bus explains to him that she makes the trip in order to find out if it's her missing granddaughter"
