After teenager Robert Piest disappears on his mother's birthday, Des Plaines Police Department officers track, interrogate and tail the contractor Piest was last seen with -- John Wayne Gacy.

Officers excavate the crawl space beneath John Wayne Gacy's home; Gacy shows Amirante, Kunkle and Kozenczak where he disposed of Rob's body; Johnny Szyc and his best friend, Lynn, venture into Uptown.

The media circus begins; Amirante questions whether defending Gacy is the right choice; the Piests cope with the reality of what Gacy did to Rob; Sam Stapleton and Randy Reffett navigate boyhood in Uptown.

A psychiatrist interviews Gacy, revealing disturbing details about his past; Tovar and Kozenczak confront the dark truths of the systemic failures that allowed Gacy to kill for so long; a love story unfolds between Billy Kindred and Mary Jo Paulus.

A blizzard buries Chicago; Kozenczak tracks down Gacy's surviving victims; Kunkle and Kozenczak attempt to break Gacy's accomplice, David Cram; Billy Carroll introduces Dale Landingin to the lucrative, but sometimes dangerous world of sex work.

In the past, an inebriated Gacy confesses to Sam the ways he groomed, sexually assaulted, tortured and killed countless boys and young men.

Kunkle and Sam are knee-deep in Gacy's trial; Tovar volunteers to drive Gacy to and from court, attempting to compel him to come clean about how many he killed; the disturbing tale of how Gacy befriended and groomed David Cram is revealed.

The life of Jeffrey Rignall, one of Gacy's few surviving victims, is chronicled; Gacy's execution day causes massive protests and reunions as victims' family members and those who worked the case seek closure; Amirante tries to move on.