A seemingly ordinary working mother secretly lives as a legendary sniper who delivers justice where the law fails. After returning from a three-year hiatus, she must balance protecting her family with eliminating dangerous criminals, all while a determined journalist and a relentless detective close in on her hidden identity.

Gu San-yeong is possessed by an evil spirit after receiving a relic of her dead father. She meets Yeom Hae-sang, a folklorist who can see ghosts and spirits, and enters a completely different world from what she once knew.