The thrilling, genre-bending conclusion to Lady Helen's demon-hunting adventures, set in the glittering Regency world. Lady Helen has retreated to a country estate outside Bath to prepare for her wedding to the Duke of Selburn, yet she knows she has unfinished business to complete. She and the dangerously charismatic Lord Carlston have learned they are a dyad, bonded in blood, and only they are strong enough to defeat the Grand Deceiver, who threatens to throw mankind into chaos. But the heinous death-soaked Ligatus Helen has absorbed is tearing a rift in her mind. Its power, if unleashed, will annihilate both Helen and Carlston unless they can find a way to harness its ghastly force and defeat their enemy. In the final book of the trilogy that began with The Dark Days Club and continued with The Dark Days Pact , the intrepid Lady Helen's story hurtles to a shocking conclusion full of action, heartbreak, and betrayal.