The Sixth Wicked Child is the third and final book in J.D. Barker's 4MK Thriller series, published in August 2019 and following The Fourth Monkey and The Fifth to Die. It brings the hunt for the Four Monkey Killer to a close by turning it inside out: Anson Bishop, the prime suspect, turns himself in and begins telling a version of events nobody in Chicago Metro or the FBI is prepared for.
Victims are discovered within minutes of each other in Chicago and in South Carolina, impossibly far apart yet plainly connected, each found with "Father, forgive me" written on cardboard nearby. For Detective Sam Porter the phrase reaches back into memories he had intentionally left behind; for Bishop it ties a childhood to the present. Around them the investigation comes apart — a hospital under lockdown, a rogue officer, and corruption reaching the top of the department.
Barker structures the finale in short, alternating chapters that move between Porter, Bishop and the other investigators, and threads diary entries from Bishop's past through the present-day manhunt so that the two timelines close on each other. The result is a fast, deliberately destabilising read, in which what the reader has been told is repeatedly revised, until the motive behind the Four Monkey killings is finally laid out.
