Because of love. In the TV series "Hou Dali's Notes on Criminal Investigation", Hou Dali and Zhang Xiaoshu experienced life and death together and developed deep feelings, fell in love and finally got married. The play tells the story that Hou Dali, an intern policeman, began to study hard because of the inexplicable death of his first girlfriend, was admitted to the University of Political Science and Law, and naturally became a policeman, vowing to find out the truth about his girlfriend's death.