What happens when ordinary people, in real-life murder clubs, set out to investigate crimes, both recent and cold cases?

The Netflix hit Don't F**k with Cats was based on the 2012 Montreal murder of thirty-three-year-old Lin Jun by his porn-star boyfriend, Luka Magnotta. Previously Magnotta had anonymously posted videos of himself killing kittens. This spurred horrified Facebook sleuths into working tirelessly to uncover his identity and location.

Other investigations include: A self-taught forensic artist, who uses computer software and coroners' photographs to help identify victims by showing how they looked when alive. The mother who swore at her murdered daughter's graveside that she would get the gang who had sprayed her car with bullets. It took fourteen years in the case of one gang member, but she finally entrapped him via the fake profile she had created on MySpace. The retail clerk turned citizen sleuth who helped to match a photo of a missing man to a skull found in a bucket, which resulted in the conviction of the victim's best friend. Websleuths matched the IP address of a suspicious contributor to a lottery-winning victim's financial advisor, which led to his body being found beneath a newly poured concrete slab in his advisor's boyfriend's garden. Sometimes citizen sleuthing goes wrong, though, with innocent people being targeted, or accused of crimes they haven't committed, with tragic results.

The real-life version of Richard Osman's The Thursday Murder Club is grittier, with intrepid amateur investigators delving into truly gruesome unsolved crimes in pursuit of justice.