Draco drinks a potion that makes him know if a person is lying, and Harry, apparently at fault that Draco is this way, is forced to 'help' him with the effects of the potion. For the first time, they deal with each other with no lies to hide behind.

A mysterious notebook. A dangerous secret. A rivalry on the brink of transformation. Harry Potter never expected much from the little green notebook that landed in his hands. Yet as he experiments with its alluring contents, it quickly becomes clear that this object holds far more power than he could have imagined. With every page he turns, Harry is pulled deeper into a dangerous game...one that could change everything he thought he knew about Draco Malfoy. Draco, has his own reasons for the notebook. What begins as a calculated manipulation soon spirals into obsession, leaving both of them more entangled with every encounter. The notebook may hold the key to their rivalry, but neither is ready for the chaos it unleashes. As the Triwizard Tournament approaches and tensions mount, the lines between hatred and desire blur, forcing Harry to confront a truth he has long avoided: some games have no rules.

Harry and Draco are both starting as Hogwarts professors at the same time. Their students quickly start to get a slightly different impression about their relationship than Harry and Draco have.