"Event Horizon: A Marine's Vietnam War Story" is a memoir of Terry Presgrove's time in the United States Marine Corps: 1967-69, boot camp through returning home after the war. The book zeroes in on operation Dewey Canyon, at which time he was the artillery forward observer for Alpha Company, 1st Battalion, 9th Marine Regiment, 3rd Marine Division. Dewey Canyon was the last major engagement by the Marine Corps during the Vietnam War. This work is an attempt to give the outside observer a peek behind the veil and some pliable understanding into what a combat Marine in Vietnam experienced. The extreme psychological impact of war on the individual combatant has been portrayed as an "event horizon," a boundary in spacetime beyond which events cannot affect an outside observer. In layman's terms, it is defined as "the point of no return," i.e., the point at which the gravitational pull becomes so great as to make escape impossible. Even light cannot escape. For those who fought in the Vietnam War, and specifically for the Marines who fought in operation Dewey Canyon, it is impossible to escape the experiences that have generated a paradox of "Revolving Door" ("The Revolving Door" is the fourth chapter of Event Horizon) memories that will forever both haunt and inspire us. In the book's concluding chapter, under the title " Unlearned Lessons of War," America's "Revolving Door" war policies are addressed. Even though more than four decades have passed since the Vietnam War, many of the same mistakes continue to be made today. The message of this work is as relevant today as what you read on your favorite news app or see on the evening news. In the "Unlearned Lessons of War" critique, the author points out some of the self-defeating policies that have trapped our great nation. Finally, In "Appendix A," Presgrove delivers a spiritual message of hope to all the wounded and hurting folks who question their relationship with God. From our old warriors to the very young, no one is exempt from feelings of hopelessness and despair.