Initial story events take place during James T. Kirk's years in the admiralty when he begins to suffer from psychological issues after reading a book Dr. McCoy gave him entitled Strangers from the Sky. This book is a recent publication which explains why the "official" records of how Human and Vulcan races met for the first time were incorrect. The book's story drives into Kirk's mind causing him to dream of the story as if he were there during the events. Psychoscans shows him to be in a mentally unstable state and when Spock is similarly diagnosed the only cure for them both is to be found in mind meld...
The meld takes them into the adventure starting with "something as simple as a stardate" from the early days of the Enterprise's 5-year mission where they "boldly go where no one has gone before."
The basic concept of this book-- in which Vulcans accidentally land on Earth years before the official "First Contact"-- is echoed in the Star Trek: Enterprise episode "Carbon Creek".
Strangers from the Sky was the first Star Trek book to be produced as an audiobook. It was read by George Takei and Leonard Nimoy. Whilst Takei read the majority of the book, Nimoy occasionally interjected in-character as Spock at certain points during the plot.