One of the few PBS Masterpiece shows that’s not based on a book franchise returns with its sixth season this Sunday, August 24. Every season of Unforgotten begins with the discovery of human remains, and the mystery unfolds from there as London detectives attempt to solve the cold case. But the deeper the truth lies, the bigger the emotional toll for the suspects, the families left behind, and for the detective inspectors themselves.

Unforgotten Season 6 begins the wetlands of east London. While detectives Sunny Khan (Sanjeev Bhaskar) and Jessica James (Sinéad Keenan) try to identify the victim and catch the killer, viewers are introduced to four possible suspects with complicated backstories.

The suspects this season are London college professor Juliet Cooper (Victoria Hamilton), Afghan immigrant Asif Syed (Elham Ehsas), young autistic man Marty Baines (Maximilian Fairley, who is autistic himself), and controversial TV commentator Melinda Ricci (MyAnna Buring).

“The intention is always to write characters that are multifaceted,” Unforgotten creator and executive producer Chris Lang told TV Insider in a Season 6 preview. “They may have done bad things, but that doesn’t mean they’re necessarily bad people.”

Keenan joined Unforgotten Season 5 as the new detective following the shocking death of DCI Cassie Stuart (Nicola Walker) in Season 4. Keenan’s first season showed a tense start between Jessica and Sunny, but their relationship has stabilized in Season 6. “Without knowing too much about each other’s lives,” Bhaskar told us, “they’ve built a degree of trust with each other, which allows them to become better partners.”

Get a look at Unforgotten Season 6’s suspects, detectives, and more in the gallery below.