As District 21 is struggling to come to terms with the loss of one of the team they are forced to put their personal feelings aside when a café is bombed. The unit has several suspects and only one good eye-witness, who happens to be a minor. Halstead pulls some strings to convince the mom to let him question Isabella (guest star Haley Seda) on what she saw. Atwater finds himself in hot water when he makes a crucial mistake. Thanks to the tech savvy Mouse (guest star Samuel Hunt) the team is able to gain important intel that could help solve the case. Meanwhile Voight helps Platt when she comes up against several roadblocks in an attempt to get a memorial stone for their fallen member.