The first season covers the first two weeks of the investigation and has three main storylines: the police investigation into Rosie's murder, the attempts of her family to deal with their grief, and the fluctuating electoral fortunes of a political campaign that becomes embroiled in the case. It stars Mireille Enos as homicide detective Sarah Linden and Joel Kinnaman as rookie detective Stephen Holder.

This season follows the continued investigation into the murder of local teenager Rosie Larsen, with each episode covering approximately 24 hours. The season culminated in the closing of the Larsen murder, with the discovery of those involved with the murder.

A year after closing the Rosie Larsen case, Sarah Linden is no longer a detective. But when her ex-partner Stephen Holder's search for a runaway girl leads him to discover a gruesome string of murders that connects to a previous murder investigation by Linden, she is drawn back into the life she thought she'd left behind.

Linden and Holder work a case about the horrifying slaying of a prominent family as they race to destroy evidence implicating Linden for murder.