Arnold Hodgkiss, a jewel thief who has come to London to steal the Crown Jewels, is dreamily casing the Tower of London when a strange man approaches him and says "The crown is large." Hodgkiss, nonplussed, replies "And very heavy", unwittingly giving the correct countersign. The man, a spy, thrusts a parcel at Hodgkiss and disappears. Hodgkiss keeps the parcel, hoping to turn it in some way to his advantage. Soon afterward, Jerry Cornell receives a new assignment: he is to discover the whereabouts of plans for "Project Glass," which have been stolen. Although the thief has been caught, the plans are still missing, and are believed to be in the hands of a fiendish Chinese agent named Kung Fu Tzu. Meanwhile, Kung is hopping mad because he never actually got the plans; they were given to Hodgkiss by mistake. The comedy of errors intensifies as Cornell tracks Kung, who in turn follows Hodgkiss, who eludes Kung but finds trouble aplenty when he tries to steal a brooch from a stall on Portobello Road.