I believe I´ve read all of this very short book. The writer has a very gentle concern about the cult of Einstein, its timing and how it grew. For the insight into the timing, if not much detail about the scientific issues in Einstein´s cosmology, worth finishing.
Mr. Coles does point out that Special Relativity, unlike Newtonian physics, does not describe objects which accelerate under the effects of gravity. Just what gravity might be and how to measure it, at least as a universal, are ongoing problems in physics.
By the end of the book, cosmologists have just discovered that objects at the greatest distance of the universe are in fact accelerating. This lead to the invention of dark energy and dark matter -- neither of which has ever really been measured -- in part to keep Einstein´s theories intact.