This is the second book in the "Time Odyssey" (as opposed to "Space Odyssey") series. This time, those aliens who messed up the world's historical times in the earlier book are back, having in the normal timeline shot a Jupiter-sized planet into the sun thousands of years ago to cause a major solar eruption and the cleansing of the solar system of human life. As the line in "2001" puts it, "And sometimes, dispassionately, they had to weed". The attempts of humanity to avoid catastrophe with a daring technological innovation are the subject of this book, a typical logical Clarke outworking of the concept. And, in a delightful twist at the end (the sort of O. Henry-like flourish that Clarke seems to enjoy) the actions of the aliens, instead of destroying humanity to purify the solar system, serve to bring them into contact with humanity in a most unexpected way.
The two books really don't hang together as a series. They have in common British Army captain Bisela Dutt, who came back from the time-splintered world of the first book via the agency of the mysterious aliens who caused the whole mess and introduces to the world (or at least the great and good of the world) the idea that the coming sunstorm is not entirely a natural phenomenon. However, independently, they are great reading for all lovers of good science fiction.