Yates left a note that he'd see Erin back home. They know he's coming to Chicago. 

Yates attacks and kills four nursing students in their apartment. 

Voight is concerned about Lindsay and wants to keep her safe. 

Halstead and Atwater learn that Yates is looking for Nellie Carr. They find another note for Lindsay which indicates he knows where she is. 

Platt is asked to handle the press. 

A package is dropped off for Lindsay at the station. They call in the bomb squad, but it's not a bomb, but it is a hand with another note. 

Yates has Nellie hostage. He tells Lindsay he'll see her soon. They realize he's in Lindsay's apartment and the find Nellie there. 

Benson and Fin arrive in Chicago. 

Benson offers to interview Nellie with Lindsay. 

They realize Nellie is Yates' sister and speak to their mother who says they put Yates up for adoption to protect Nellie. 

Voight makes Lindsay stay at the station. 

Yates calls her and tells her to come see him alone or he'll kill Nellie's father.

He tells her about his early kills and says they're similar. 

He kills his hostage and baits Lindsay into shooting him. 

Benson tells Lindsay about William Lewis at Molly's.