Chicago P.D. (2014)

S04E15 Favor, Affection, Malice or Ill-Will

Lindsay receives a lead about a father consumed by grief who is seeking revenge for his daughter's murder. To get closer to the situation, Olinsky poses as a hitman. Since Gang Intelligence doesn’t have sufficient proof to take down the initial suspect, the team decides to revisit the case for more clues. In the meantime, Ruzek returns after completing his undercover mission, only to find that Voight has reassigned him to patrol duty.