The priceless Blue Water sapphire is coveted by the heirs of Sir Hector Geste: his new wife Flavia; his daughter Isabel; and his adopted twin sons, heroic Beau and pathetic Digby. When Sir Hector takes to his deathbed (where he remains for the duration of the film), Beau absconds with the stone to keep it from his stepmother. Flavia pursues him to North Africa, dispensing sexual favors to promote her schemes.