Olivia gets used to being Noah's new foster mother and a new member of the squad has a difficult start. 

Sergeant Benson searches for the true killer of Noah's mom, Ellie, as she encounter's last season's Little Tino once again. Detective Amaro, after being bumped down to the traffic beat in Queens, encounters an underage prostitute which gives Benson the longawaited opportunity to pursue the leader, the pimp responsible for carrying out Ellie's horrific death and orphaning Noah. 

A new recruit, Detective Dominick "Sonny" Caresi Jr, is the opposite of what Benson requested, but his well-intentions seem to keep him in check. 

The squad approach the problem from many different ends, trying to obtain testimonies from the likes of Tino as well as the underage prostitute, Luna Garcia, in an attempt to bring Ellie's murderer to justice. They are duped, however, at almost every turn - even when they run some pretty sly tricks of their own, using Fin and Amaro in an attempt to find a way into the ring and the leader's inner circle. 

Ultimately, there is closure to be found for Olivia Benson, and she pursues that promise to catch the culprit in honor of not only Ellie, but her new son and their future together.