I'm only at the end of Chapter 3 of the book and there's no doubt that Tom Holland is a master scholar who has done an impressive amount of research and knows his subject well.
BUT... I know that people on this site are mainly interested in the origins of Islam, but what I question are Holland's personal assumptions about the existence of Jesus. He seems to accept without question that Jesus existed and that the stories of his life and death are based on truth and fact.
On page 155, for example, he says, "A few decades on from Jesus' crucifixion...". Where is the evidence of Jesus' crucifixion? Why does he treat Jesus as a real person when most [non-religious] scholars can demonstrate that it's highly likely he wasn't, or at least that he wasn't who we think he was.
For example, "No one has the slightest physical evidence to support a historical Jesus; no artifacts, dwelling, works of carpentry, or self-written manuscripts. All claims about Jesus derive from writings of other people. There occurs no contemporary Roman record that shows Pontius Pilate executing a man named Jesus. Devastating to historians, there occurs not a single contemporary writing that mentions Jesus. All documents about Jesus came well after the life of the alleged Jesus from either: unknown authors, people who had never met an earthly Jesus, or from fraudulent, mythical or allegorical writings."
And, "If, indeed, the Gospels portray a historical look at the life of Jesus, then the one feature that stands out prominently within the stories shows that people claimed to know Jesus far and wide, not only by a great multitude of followers but by the great priests, the Roman governor Pilate, and Herod who claims that he had heard "of the fame of Jesus" (Matt 14:1)". One need only read Matt: 4:25 where it claims that "there followed him [Jesus] great multitudes of people from Galilee, and from Decapolis, and from Jerusalem, and from Judea, and from beyond Jordan." The gospels mention, countless times, the great multitude that followed Jesus and crowds of people who congregated to hear him. So crowded had some of these gatherings grown, that Luke 12:1 alleges that an "innumerable multitude of people... trode one upon another." Luke 5:15 says that there grew "a fame abroad of him: and great multitudes came together to hear..." The persecution of Jesus in Jerusalem drew so much attention that all the chief priests and scribes, including the high priest Caiaphas, not only knew about him but helped in his alleged crucifixion. (see Matt 21:15-23, 26:3, Luke 19:47, 23:13). The multitude of people thought of Jesus, not only as a teacher and a miracle healer, but a prophet (see Matt:14:5).
"So here we have the gospels portraying Jesus as famous far and wide, a prophet and healer, with great multitudes of people who knew about him, including the greatest Jewish high priests and the Roman authorities of the area, and not one person records his existence during his lifetime? If the poor, the rich, the rulers, the highest priests, and the scribes knew about Jesus, who would not have heard of him?
"What appears most revealing of all, comes not from what people later wrote about Jesus but what people did not write about him. Consider that not a single historian, philosopher, scribe or follower who lived before or during the alleged time of Jesus ever mentions him!"
(Source:
http://www.nobeliefs.com/exist.htm)
So I am looking forward to hearing what Holland has to say about Islam and Muhammad, but I have less confidence in what he purports to be fact now than I did when he started. I think he also cites the Constitution of Medina (622 AD and usually considered to be the first authentic reference to Muhammad) as a historical fact when again, there is no evidence for this.
What is very clear, though, is that what we believe to be historical facts - everything we have based the history of the modern world on - is in reality stories invented by political and religious individuals who wanted to corrupt the realities of the past and make themselves appear to be of great / divine lineage.
That is a revelation to me, and the implications are huge.