It's every parent's worst nightmare. When a mum goes to pick up her son from a playdate, the woman at the door claims to have never heard of him.

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, and 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.