The primary conflict of Susan E. Hinton's novel, That Was Then, This Is Now, eventually comes down to the changes that are occurring between the inseparable friends, Bryon Douglas and his foster brother, Mark. Two events cause the irreparable split between the two lifelong pals: After Mark gets Angela drunk and cuts off her hair, her two brothers--Tim and Curly Shepard (of The Outsiders)--confront Bryon and beat him senseless. His refusal to tell the Shepards that it was actually Mark who is responsible for their sister's unwanted haircut causes Mark to feel he now owes Bryon a debt that he can no longer pay.
Later, in Chapter 10, while searching for a cigarette, Bryon discovers Mark's secret drug stash and realizes that he has been dealing drugs in the hippie house where M&M has been staying. In a moment of decisiveness, Bryon calls the police and reports Mark. Mark is arrested and taken to jail--forever ending the friendship between the two boys.