Desperate to catch infamous art thief MARRASCAUD, the Metropolitan Police build what they imagine is a perfect trap. The Le Mesurier family are to announce the society debut of their beautiful daughter LUCINDA, who will be wearing an exceptionally expensive diamond necklace. On display will be 'Hercules Vanquishing the Hydra', a priceless work by Marrascaud's favourite artist Van Druys. Last but not least, the great HERCULE POIROT will be in attendance. How can Marrascaud resist? The results are catastrophic.