Twelve. (The Danilov Quintet 1)

On 12th June 1812, Napoleon's Grande Armee forded the River Niemen and crossed the Rubicon - its invasion of Russia had begun. Charged with delaying the enemy's inexorable march on Moscow, a group of Russian officers summon the help of the oprichniki, a band of mercenaries from the outermost fringes of Christian Europe. As rumours of a plague travelling west from the Black Sea reach the Russians, the Oprichniki - twelve in number - arrive.
Preferring to work alone, and at night, they prove brutally, shockingly effective against the French. But one amongst the Russians, Captain Aleksei Ivanovich Danilov, is unnerved by the mercenaries' ruthlessness...and as he comes to understand the true, horrific nature of these strangers, he wonders at the nightmare they've unleashed in their midst...