Carbon Grey Series by Paul Gardner, Hoang Nguyen, Khari Evans, Kinsun Loh

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. When the Kaiser is found dead Giselle is accused of his murder. Pursued by her sisters and hunted by the enemy, Giselle must unravel the prophecy of the Carbon Grey before history itself is rewritten.

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.

Grey, 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.

LEGEND OF THE GREYS The Sisters Grey are warriors, sworn to protect their Kaiser. But as a great war rages, the Kaiser is found dead, and one sister--Giselle Grey-- is accused of his murder. Pursued by enemies, Giselle must unravel the prophecy of the Carbon Grey--before history itself unravels. This collection includes all three volumes of the epic saga, stories from CARBON GREY: ORIGINS, and a new ten-page prologue.