In April of 1798, Napoleon appoints Lieutenant Charles MacDonald, a nineteen-year-old graduate geographical engineer, to be the pathfinder for his personal Brigade of Guides during the invasion of Egypt. Charles was born in Virginia during the American Revolution and was educated in France, a graduate of L'Ecole Polytechnique and a postgraduate of L'Ecole des Ponts.
But agents of the British Secret Service who are trying to undermine the invasion of Egypt interfere in Charles's journey on a number of occasions by attempting to rob the mail coaches he is accompanying.

In response, General Bonaparte assigns Charles's father, the blind General James MacDonald, his confidant and instructor in engineering and mapmaking at L'Ecole Militaire more than a decade earlier, to head a secret section investigating the British and these crimes. What they uncover is an abandoned convent in Paris being used as a headquarters--with 3.5 million francs in gold hidden in its walls.