Spenser: For Hire S01 E15 Brother to Dragons

"A lot of people think I like to get even. They're dead right."

Spenser is going skiing with Susan, but when he picks her up at Smithfield High School where she works, he finds out one of her students died of a heroin overdose. Spenser gets hired by the superintendent and goes undercover as a teacher at her school to find out where the drugs are coming from. He obviously gets into it with the dealers.