The TV series "The Oath" is directed by Mao Weining. The main plot tells the story of Yan Shaobai, a mathematical genius who bears family hatred and hates the Japanese invaders during the Anti-Japanese War. By chance, he met officer Xiao Siyu and gangster Lei Hu and formed a brother of different surnames. In a battle, Xiao Siyu's head was hit by shrapnel, which affected his ability to deduce as an expert in "war chess deduction", so he found Yan Shaobai to be his successor. Yan Shaobai used his mathematical talent and the help of Xiao Siyu to become a master of war chess. After a series of reviews by Ono, he finally mixed into the Japanese army and cooperated with expert Kato Hirofumi to complete the development of the weapon system of the "Black Dragon" plan, and successfully saw through the Japanese's insidious combat plan, disrupting the careful deployment of the Japanese army. During this period, Yan Shaobai and Han Yixuan fell in love with each other, but they were unable to be together due to misunderstandings, and Xiao Siyu also died due to years of injuries and overwork. The third brother Lei Hu cooperated more and more with the Japanese, and his path went further and further astray. Finally, under the persuasion of his two elder brothers, he returned to the right path and died while rescuing Han Yixuan. Yan Shaobai and Han Yixuan resolved their misunderstanding and became lifelong partners.