HRH Princess Margaret is due to visit Oxford to unveil the British Imperial Electric Company's latest weapon of mass destruction at a Cowley factory. Endeavour who is still stuck doing General Duties, is excluded from the event. After the ceremony comes to a close he finds himself deeply embroiled in the affairs of the factory and its owners, the dysfunctional Broom family. Percy Malleson, has been found cuddled in a secluded area of the shop floor in the factory. One of his hiss colleagues, Lenny Frost, is the main suspect as there is bad blood between them resulting from an industrial accident.