Marissa Irvine arrives to collect her young son Milo from his first playdate, but the woman who answers the door isn't a mother she recognizes and doesn't have Milo, beginning every parent's worst nightmare.

As Detective Alcaras investigates Milo's disappearance, Marissa, with Jenny's help, works hard to raise awareness; a press conference turns ugly when questions are asked about the Irvines' past business dealings

Alcaras turns his attention to the recent Chicago Marathon, attended by Carrie, the Irvines and a potential new suspect; a canvassing event aims to keep the case alive; Peter takes matters into his own hands.