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.

Alcaras struggles to balance work and home life and must make a difficult choice when he's tempted by an offer that goes against his morals. The police struggle to connect the mystery marathon man with Carrie and Milo.

News from Alcaras concerning Carrie's hideout throws suspicion on all of the Irvines. Brian uncovers a betrayal from Peter, who accuses Lia of lying. A long-buried family secret threatens to tear the Irvines apart.

The Irvines struggle to adjust to their new normal, while also recovering from the fallout of their arguments. As Marissa tries to cope with past events, Jenny deals with domestic pressures of her own and uncovers some of Richie's secrets.

Years after suffering a tragedy, a chance encounter with a young Milo leads Carrie to fixate on the boy. Her obsession takes a dark turn while planning the kidnapping, forcing her to ask for help when things go awry, with deadly consequences.

Reeling from the recent home invasion, Marissa tries to put the pieces together to learn the truth. As Peter comes clean, she must decide how to protect the family. Alcaras hones in on the truth before being forced to make a tough decision.