Sundiver (1980) is the first book of David Brin's Uplift Series, which continues on with Startide Rising, The Uplift War, and then the three book saga of the planet Jijo, Brightness Reef, Infinity's Shore, and Heaven's Reach.
Sundiver focuses on Jacob Demwa, a relatively young widower who is called away from his work with genetically enhanced neo-dolphins in order to participate in the "Sundiver" mission. Sundiver's ostensible mission is to explore the upper portion of the Sun's photosphere and comminicate with strange creatures that seem to live there. But the mission is also undertaken in order to prove that human technology was still worth pursuing, even after the introduction of the Galactic Library, which contains the technology of a billion years of galactic civilization.
The plot of the book revolves around the mystery of the events of the Sundiver mission, starting with the mysterious failure of one of the probe ships, killing a genetically enhanced neo-chimpanzee scientist. This mystery is projected against the larger mystery of the entire Uplift Series, which is, who, if anybody, uplifted mankind?
This book provides an entertaining introduction to the series and Brin's universe, but is not as good as the next two. It can be skipped, but there are some references in the later books that you will not understand.