Usurper takes place in an alternative timeline of 1898 in London. The outer worldly Citadel has landed in the city causing massive panic and releasing the maddening Fog. Recently re-crowned Empress Eleanor has assembled the royal forces and her four most loyal Knights to enter the Citadel - in the hopes of learning more, and hopefully finding a way to rid London of this terror. Meanwhile, Waltham, the leader of the Veimar, uses his own forces to ascend the Citadel and challenge the Navigator for his own...purposes...