In A Brig of War, Nathaniel Drinkwater is promoted lieutenant of the brig Hellebore. He finds routine convoy escort duties end abruptly when Admiral Nelson, pursuing the French fleet to Egypt, sends Hellebore to the Red Sea with an urgent warning to the British squadron More...there. However, Nelson's apprehensions over French ambitions in the East are more than justified. Edouard Santhonax, Drinkwater's old enemy, is already preparing for a French descent on India.

The hunt for this elusive Frenchman and his frigate is combined with British naval operations on the flank of Napoleon's Egyptian campaign. It is during the attack on Kosseir that Drinkwater is left for dead. His escape and the subsequent desperate attack on Santhonax leads to a still more dangerous situation under Augustus Morris, former tyrant of the midshipmen's berth on HMS Cyclops.

Drinkwater's fight to bring a half-armed ship safely to the Cape of Good Hope is beset with personal enmity, the activity of the French and the violence of the sea.