Kang Dong-goo [Lee Je-hoon] is a gifted grave robber known in the underworld for his uncanny intuition in locating hidden burial chambers and relics. Operating around Seoul, he relies on instinct and improvisation rather than formal archaeological training. He lives with veteran digger Ju Jin-mo Man-gi, who taught him the craft, and Man-gi’s tech-savvy daughter Park Se-wan Hye-ri, who provides logistical and hacking support. During his heists, Dong-goo leaves behind the wrapper of a chocolate pie as a personal calling card whenever he escapes with an artifact.
After stealing a valuable Buddha statue from a temple that was under police protection, Dong-goo approaches wealthy antiques broker Song Young-chang Sang-gil to fence the item. Impressed by Dong-goo’s daring and talent, Sang-gil strikes a deal to handle his future finds and soon commissions him to obtain a mural from a Goguryeo-era tomb. To pull off the more complex tomb robbery, Dong-goo recruits Dr. Jones Jo Woo-jin, a specialist in ancient tomb murals who can decipher layouts and hidden passages.
Sang-gil is revealed to be a secret collector who has amassed a large private hoard of illegally excavated antiquities, stored in a heavily fortified vault and managed with the assistance of museum curator and antiques expert Yoon Se-hee Shin Hye-sun, who helps authenticate and quietly move the pieces.
Through flashbacks, it is revealed that years earlier Sang-gil hired Dong-goo’s father for a tomb robbery, then murdered him and attempted to bury a young Dong-goo alive, leaving him a chocolate pie as a final “gift” before sealing the grave. Dong-goo survived, but the betrayal left him with a deep desire for revenge. In the present, he continues to work for Sang-gil while secretly plotting to bring him down.
When Dong-goo persuades Sang-gil that a legendary royal sword from the tomb of King Seongjong may still lie hidden beneath central Seoul, the two men agree on a high-stakes heist: Dong-goo will lead an expanded crew—including legendary shoveling master Sapdari, nicknamed “Shovel Leg” Im Won-hee—to tunnel into the underground site and recover the weapon before the authorities or rival criminals can interfere.
Kang and his team eventually reach the royal tomb, but the job is only part of Kang's larger plan to take revenge on Sang-gil for murdering his father years earlier and attempting to bury Kang alive. After luring Sang-gil into the tomb on a false promise of a hidden royal sword, Kang abandons him underground and leaves him with a chocolate pie, mirroring the way Sang-gil once left Kang for dead. Sang-gil is later discovered and rescued by the legitimate refurbishment crew, only to find that his carefully guarded private collection has been cleared out. Se-hee, who has secretly shut down Sang-gil's security system to steal his hoard for herself, is shocked to discover that Kang has already emptied the vault, leaving behind only a portrait.
It is revealed that while Kang's crew were tunneling toward the royal tomb, Man-gi [Ju Jin-mo] and Hye-ri [Park Se-wan] dug a separate tunnel to Sang-gil's vault, working with police officer Chief Oh [Park Jin-woo] to recover the stolen antiquities and return them to museums. Kang's crew keeps Sang-gil's cash for themselves, while the public credit for the recovery of the artifacts is given to Se-hee, who was thoroughly tricked.
