"The Best Friend" revolves around the complex relationship between Doan Nhuoc Nam, Phan Hieu Vy, and Le Tieu. Initially, Nhuoc Nam and Hieu Vy were inseparable best friends. However, when living under the same roof with her boyfriend, Hieu Vy discovered the clandestine and forbidden relationship between Le Tieu and herself. This revelation strained the sisterly bond between Nhuoc Nam and Hieu Vy, ultimately leading to its demise. After parting ways with Nhuoc Nam, Hieu Vy begins to develop new feelings for Le Tieu. However, this newfound connection only lasts for a fleeting moment. Hieu Vy gradually reveals her controlling and twisted nature towards Le Tieu, causing him constant pressure. Meanwhile, Nhuoc Nam and Le Tieu unexpectedly cross paths again, further entangling their complicated love triangle. Le Tieu grows tired of Hieu Vy's manipulation and desires to reunite with Nhuoc Nam, proposing a breakup with Hieu Vy. On the other hand, Hieu Vy blames all her sins on Nhuoc Nam's head and is determined to join his new company to execute her revenge plan. The story in "The Best Friend" continues to revolve around the schemes, plots, and intricate emotions among these three main characters.