The story of this book is quite complicated. I haven't read the whole book, but I can answer your question based on some information I know. According to what I know, the story of the book 'Buy One, Get One Free' begins in the second chapter,'Suman's Betray'. In the second chapter, White Night and Suman began a love story and their relationship gradually became complicated. After the second chapter, the story began to involve the relationship between Ye Ningyuan, Xu Nuo, and other characters. To be specific, Ye Ningyuan and Xu Nuo's story began to appear in the fourth chapter,"The Truth", while Bai Ye and Su Man's story ended in the fifth chapter,"The Wedding". Therefore, the story of the buy one get one free for hundreds of millions of brides had already begun from the second chapter," Suman's Betrayal."