Fitzgerald is not a Bible scholar, so take this book with a grain (but only a grain) of salt, the same way you'd read a science book written by someone who's a science popularizer rather than a scientist.
Although the view he presents, that Jesus Christ is entirely mythical, is far from mainstream, it seems defensible.
For one thing, as he takes pains to explain, entire field of Bible studies tends to attract people who already believe that Jesus is real, and is thus biased in that direction. But if scholars like Bart Ehrman, Richard Carrier, and Robert Price can be believed, and I think they can, solid historical evidence is in very short supply.
All in all Fitzgerald does a good job of presenting reasons to think that the gospels have been copied, recopied, edited, and adapted from earlier stories that, once you strip away the myths, exaggerations, and forgeries, there's no real core left.