Star Trek: Strangers from the Sky

In the twenty-first century: Years before the formal first contact that would be recorded in Earth's history, a Vulcan space vessel crash-lands in the South Pacific, forcing humanity to decide whether to offer the hand of friendship, or the fist of war. Complicating matters is a second visitation: a group of people from two hundred years in the future, who serve on a starship called Enterprise....
In the twenty-third century: A new novel called Strangers from the Sky reveals the truth about this heretofore unknown first contact. Reading the novel leads to nightmares that torment Admiral James T. Kirk -- dreams of his dead comrades, Gary Mitchell, Lee Kelso, and Elizabeth Dehner, from his earliest days aboard the U.S.S. Enterprise™; visions of a forgotten past in which he somehow changed the course of history and destroyed the Federation before it began.