When Chen Yongfu, a senior engineer of a certain unit in City A, and his girlfriend, Qin Yufan, an accountant of the same unit's financial office, were actively planning their wedding, he accidentally got drunk and had sex with his sister-in-law Qin Yunan, and became pregnant as a result. Qin Yufan gave his fiancé to his sister for the sake of her sister's honor. Later, due to emotional discord, Qin Yunan finally returned the fiancé who originally belonged to her sister to her sister.