In the novel, Moorcock weaves an existentialist tale about Karl Glogauer, a man who travels from the year 1970 in a time machine to 28 AD, where he hopes to meet the historical Jesus of Nazareth.

The story begins with Karl's violent arrival in the Holy Land of AD 28, where his time machine, a womb-like, fluid-filled sphere, cracks open and becomes useless.

In numerous interpolated memories and flashbacks, Moorcock tells the parallel story of Karl's troubled past in 20th century London, to explain why he is willing to risk everything to meet Jesus.

Since the Essenes witnessed his miraculous arrival in the time machine, John decides Karl must be a magus, and asks him to help lead a revolt against the occupying Romans.

Karl, however, is so deeply committed to the idea of a real, historical Jesus that, at this point, he himself begins to step into the role, gathering followers - carefully choosing ones whose names are identical with those attested in the Gospels, repeating what parables he can recall, and using psychological tricks to simulate miracles.