Koko is a horror-mystery novel by American writer Peter Straub, first published in the United States in 1988 by EP Dutton, and in Great Britain by Viking.

During a reunion of veterans at the Vietnam Memorial in Washington, D.C., four survivors of a doomed platoon—Michael Poole (a grief-stricken pediatrician), Tina Pumo (owner of a Vietnamese restaurant), Conor Linklater (an itinerant construction worker) and Harry Beevers (an opportunistic lawyer)—gather to discuss the killings.

While wandering around a residential area of Bangkok, Poole comes across Underhill at a small neighborhood fair and realizes that he is too stable and good-natured to be the killer.

The group, now including Maggie, deduce that the killer is Victor Spitalny, a member of the platoon who vanished in Bangkok following the death of another soldier, Manny Dengler, after the war.

When the group returns to New York, Underhill is arrested thanks to an anonymous tip to police by Beevers, who wants to capture the killer alone and take all the credit for himself.

[2] He settled on the idea of Koko's murderous Vietnam veteran, and then wrote and re-wrote, ultimately completing the project after four years.

[1] He says that while writing it, he tried to mimic the "transparent" and "antiseptic" style of two stories from his collection Houses Without Doors: "Blue Rose" and "The Juniper Tree".