Chicago PD S04 E21

Season 04, Episode 21 – “Fagin”
When the team is called to an in-progress bank robbery, they come across a Robbery-Homicide detective trying to take over the crime scene; and, as the robberies continue, Lindsay makes a decision that unveils a surprising suspect behind the mask. While working on the case at the district, Upton is shocked to come across Platt, who has a special connection to her past.