"I want to join the Barmuth family and help bring down criminals. Please accept me as your daughter-in-law!" Isabella, who lost everything and was poisoned to death, wakes up to find herself back at the age of nine before her marriage is arranged to the Rosamund family. To avoid marrying into the them, Isabella sets her sights on becoming the daughter-in-law of Callahan Barmuth, the infamous "mad dog" of the Empire. Though Callahan initially keeps Isabella at arm's length, worried for her safety, her warm presence eventually melts the hearts of the entire Barmuth family, including Callahan’s son, Yuta Barmuth. But the Rosamund family isn’t ready to let go so easily—they're prepared to relentlessly pursue Isabella, determined to steal the Radgrun crown she possesses.