The fate of the British Army rests on a single shot.

In the darkest days of the Peninsular War, the Duke of Wellington is struggling to contain the French. With his regiments in disarray, falling back to Portugal, he sends his spymaster to discover the source of the enemy's strength.

When his man returns with news that a deadly factory based in Zaragoza is pumping out a seemingly inexhaustible supply of gunpowder, Wellington knows he needs an elite sharpshooter to take out the maniacal French chemist in charge.

Step forward Thomas Plunket of the 95th Regiment, the "hero of Cacabelos", who is famous for making the impossible shot. He's ordered to take three men on a desperate race against time, to assassinate the chemist—or die in the attempt.