On Jane Friedman site:

In crime fiction, the most powerful moments often aren’t about car chases or shootouts—they’re about impossible choices. Think of Martin Scorsese’s The Departed. At the climax, undercover cop Billy Costigan (Leonardo DiCaprio) faces off against corrupt officer Colin Sullivan (Matt Damon). Costigan has proof Sullivan is a mob mole; unfortunately for him, his cover’s blown too. Both men have a decision to make—cling to their oaths or focus on staying alive. Neither option comes easy, and whichever path they take, both moral and ethical consequences follow.

These are the crossroads we construct as thriller writers. They’re neither black nor white; they thrive in the gray spaces that test characters’ mettle, deliciously unsettle readers, and propel plots into uncharted territory. Incorporating these dilemmas into your narrative can evolve a simple crime yarn into something truly memorable.