An entanglement in a New York speakeasy leads Arthur Lane—heir to a lineage of vampire hunters—to cross paths with the very target he is slated to assassinate the following day: the newly ascended vampire duke, Noah Vayne. A bullet fired across a manor dining table misses its mark, yet a pact is sealed in blood, binding the palms of the two men together. This "Obsidian Vow" ties the lives of hunter and prey; should one perish, the other must follow. Forced to reverse course, Arthur finds himself in an uneasy alliance with the man he spent the previous night with—now his partner in unearthing the dark history between the late Duke Edmund Vayne and the Council. Little does Arthur know, however, that a pair of gloved hands is already lurking in the shadows, orchestrating his every move.
