The Sixth Wicked Child is the third and final book in J.D. Barker’s 4MK (Fourth Monkey Killer) trilogy, a dark and complex serial killer thriller that concludes the story of Anson Bishop. The plot follows Chicago Metro and the FBI as they deal with a hospital lockdown, a rogue officer, and corruption, all while Bishop turns himself in and reveals a shocking backstory through diary entries that detail abuse and a potential sex-trafficking ring, complicating the investigation and leading to a major twist. The book is praised for its suspense, shocking twists, and its exploration of whether a serial killer can be made, tying together the series with a conclusion that re-examines the characters and their motives.