Do Do Hee (Kim You Jung), heiress of the Future Group, crosses paths with Jeong Gu Won (Song Kang), a devil known for sealing deals that damn humans to hell. When Gu Won unexpectedly loses his powers to Do Hee, their fates become entangled. Now, Gu Won must reclaim his abilities while protecting Do Hee from her enemies, who are intent on her demise. Amidst the chaos, they devise a plan – a mutually beneficial contractual marriage. This K-drama has it all: from enemies-turned-lovers, slow-burning romance, and contractual relationship, to murder mystery, fantasy elements, and heartwarming family dynamics.