The Equalizer S04E02 - Sea of Fire

When some students at an inner city school get the blessing of a criminal to do whatever they want there, they start by assaulting one of the female students. When one of the students informs the principal what is happening to the girl, she then calls McCall for help. The student who told her about the assault is stabbed. McCall starts by being a new teacher and he takes the students who assaulted the girl to an autopsy and then has a man whom he knows "died" talk about what happened to him during his near-"death".