Guest is the heir(ess) to a grand mansion. A massive fortune left by their grandfather is hidden somewhere on the grounds, and only Guest knows where. Furthermore, the mansion is rigged with secret passages and various contraptions. A girl named Mint is hired as a new maid at the estate. However, her true identity is an assassin targeting the secret of the inheritance. She has infiltrated with the mission to locate the safe and eventually eliminate Guest. However, Mint is pathologically clumsy. She drops knives, blurts out explanations of poisons, and constantly confuses sugar for salt while cooking. Despite this, she is an unbalanced genius who possesses top-tier skills in infiltration, disguise, and combat. Furthermore, other assassins targeting Guest begin to move in the shadows. Mint's path forward, struggling to hide her mission while fending off rivals, is full of ups and downs. This is a dangerous, noisy, and somehow heartwarming comedy about a clumsy, kind-hearted assassin and their young master/mistress.