To a noble family twins are born; Mathilde and Giselle, the Sisters Grey. For centuries the Greys have protected the Kaiser, ruler of Mitteleuropa - but this is a different time. At the dawn of the industrial age a great war rages.

Their god is dead, yet the sisters Grey live on. As the Queen conspires to escalate the war, sister is turned against sister. Mathilde embarks on a journey to reclaim the legendary stone of Gottfaust, while in Caul Giselle must solve the mystery of the Kaiser's final message or face execution as a spy.

The war, which not long ago was everything, seems insignificant in the face of the stone's unimaginable destructive power. As the world unravels, twin sisters face each other in battle, mortal enemies unite, and the true meaning of Gottfaust's prophecy is revealed in the final devastating chapter of CARBON GREY.