Elena, heir to a wealthy New York dynasty, is usurped by her own clan. Cornered with nowhere to turn, she awakens Samuel, a demon sealed for a thousand years, and strikes a blood pact to save her life. While fighting Victor, who schemes to seize her family fortune, and evading the Holy Shield Organization hunting them both, she uncovers a parasitic trap hidden within the contract. Refusing either annihilation or submission, Elena takes a desperate risk to restructure the pact, breaking free from her fate as a "vessel of the Abyss" and mastering dark power of her own. She ultimately defeats all villains and mends the rift in reality. Stripped of his demonic identity, Samuel loses all memories of his past. Freed from every chain, the two begin anew, meeting and falling in love all over again.
