4MK Books in Order

The 4MK series follows Chicago detective Sam Porter and his team as they hunt a serial killer known as the Four Monkey Killer, whose crimes are built around the old see no evil, hear no evil, speak no evil, do no evil proverb.(jdbarker.com)

Over the course of three books, Barker blends police procedural work, psychological cat and mouse games, and disturbing glimpses into the killer's past. The investigation shifts between frantic searches for missing victims and diary entries that slowly reveal how a child could be shaped into a monster.

The Fourth Monkey opens with a man killed by a bus while carrying one of the killer's trademark white boxes containing a human ear. Porter discovers a handwritten diary on the body and realizes 4MK had already taken a new victim, forcing the team to read the diary in real time as they race to find a girl who may still be alive.

In The Fifth to Die, a girl is found frozen under the ice of a Chicago lagoon even though forensics show she drowned in salt water, and her clothes belong to another missing teenager. As more girls vanish, the case points toward a new predator, even as Porter secretly pursues Anson Bishop, the man he believes stands at the center of the Four Monkey murders.

The Sixth Wicked Child closes the trilogy with parallel killings in Chicago and South Carolina, cryptic messages about evil, and a hospital under siege. Anson Bishop turns himself in and offers a story that may finally explain who the Four Monkey Killer is and why the murders began, though every answer comes wrapped in new doubts about memory and manipulation.(simonandschuster.com)

Across the trilogy, Barker leans into big twists and shifting loyalties, but he also spends time with Porter's tight knit squad and their bruised personal lives. The books are gritty, sometimes graphic, and heavily serialized, so they work best when read in order, starting with The Fourth Monkey and moving straight through to The Sixth Wicked Child.{