666 is a novel. Therefore much of it should be considered fictional. However, what this story is based on is from the Bible itself and should be considered factual in those situations.
First event depicted is the rapture of believers from the earth where Christians go to meet Jesus Christ in the air as He appears to take them to heaven with Him. This event is followed by a period of seven years called the tribulation period, marked especially at the halfway point by the Abomination of Desolation committed by the Anti-christ, named Brother Batholomew, denoting the beginning of the Great Tribulation period spoken of in the book of the Revelation.
Using the technologies of the day, the Anti-christ will create a common market bringing all humans under his control for both commerce and religion. Ultimately, he becomes a world dictator, with the goal in mind of standing against God and his judgment of the earth.
The mark of 666 will be the key to the story as mankind will receive this mark in order to be able to do business, travel and any host of normal functions that they seek. Those who become Christians and resist the "mark" will be punished and in some cases even killed for their unwillingness to submit to the Anti-christ's reign.
Suspense is the element that permeates through this story which depicts the suffering and terror inflicted by this world leader on his subjects.