I read the book again wanting to really like it. McCollum was a very active hard SF writer in the 1980s and 1990s, at least from my young perspective as I bought interesting-looking new titles in used book stores on Prince Edward Island. His bibliography in his German Wikipedia article is extensive. (Curiously, the article has no English-language counterpart.)
The ideas behind The Sails of Tau Ceti is certainly audacious. Centuries after the mysterious nova destroyed Tau Ceti that 25th of August, 2001, the inhabitants of our industrialized solar system detect a light sail craft apparently pushed into interstellar flight by the light of the nova. Starhopper, the first prototype starship, is repurposed to intercept the craft before it enters our solar system. Carrying, among others, the software engineer Tory Bronson, they rendezvous with the craft only to discover that it is a crewed vehicle, an O'Neill-type habitat housing tens of thousands of hexapodal Phelans fleeing the ruin of their home system and seeking succor in ours. Bronson is convinced to represent the refugees and their case to humanity.
This habitat is just the vanguard of tens of thousands of more habitats light-months behind, carrying with them a total of three billion Phelan refugees. If they're refused settlement rights in Sol system, then they'll leave reluctantly. Humans wouldn't want them to leave, though. The Phelans had to flee Tau Ceti in the first place because a radical faction among them accidentally triggered their star's nova. In order to avoid the stranding of the fleet deep in interstellar space and the extinction of their portion of the Phelan species, they will make Sol go nova. Can Troy Bronson bridge the gap between the two species and prevent this catastrophe?
A minor kibbitz. The Phelans are noted as sending ships not only to our solar system but to Epsilon Eridani, Epsilon Indi, and Alpha Centauri, in other words the three closest Sun-like stars to our own planetary system other than lost Tau Ceti. Looking at the Internet Stellar Database, the Phelans had other options: Omicron 2 Eridani, or 40 Eridani, is closer to Tau Ceti than Epsilon Indi (10.2 light years versus 11.5), while 82 Eridani is just two thousand astronomical units further from Tau Ceti than Sol (both roughly 11.9 light years from the Phelans' home system). Especially if the pre-nova Phelans were aware of humanity through our radio pollution and uncertain about our attitudes towards alien refugees, in-universe wouldn't the Phelans have explored other, potentially safer, options. (I'm guessing that the data on the location of Sun-like stars in the neighbourhood of Tau Ceti that's a simple Google search in 2013 was more problematic 21 years ago.)
One review says that The Sails of Tau Ceti is "[n]ot exactly a usual first contact story, not exactly a usual alien refugee story, not exactly an alien invasion story." This is true. Desperate alien refugees demanding a place to live in our solar system is a trope that has frequently appeared in science fiction. McCollum's sketch of a solar system on the verge of starflight, industrialized and colonized but still dominated by a populous and habitable Earth, is plausible. Further, the character of Tory Bronson has a lot of potential. Leaving aside the entirely plausible profession of software engineer, trained to ensure that the different programs of a very complex long-range space mission work together without causing an abort-retry-fail scenario, and the drama inherent in her position as the only being who can prevent a catastrophe that would consume the lives of billions, the computer chip networked with her brain gives her unusual potential.
The problem is that this novel is not particularly anything. I may have been more credulous when the book came out, but re-reading the novel it didn't seem credible that McCollum would go to great lengths to detail human and Phelan civilization and then not find a way to save both from annihilation. If there was a final, frankly understandable, breakdown of human-Phelan relations, then Tory Bronson and everyone and ever place she knew would have been destroyed without leaving any legacy, and the experience of reading the novel would have been pointless. Tory Bronson could also have been a more compelling character, but her two different love interests and the unusual mental capacities granted her by her computer implants were barely touched upon other than to introduce him. (It wouldn't be fair to criticize McCollum, writing in 1992, for not developing Bronson's relatively rare computer implants into a more thoroughly transhumanist imagining of the future.) Even the Phelans, as physically distinctive as they were, seemed to be hexapodal humans, with only lip service lent to the ideas that the veneer of human culture adopted by the first Phelans to enter the solar system is just that, and that the Phelans are fundamentally not human.
To a considerable extent, The Sails of Tau Ceti felt like it was only the introduction to a much broader and potentially more interesting universe. In the novel's final passage, with a preliminary human-Phelan accord behind her, Bronson imagined what the new human-Phelan civilization might accomplish, imagining the new bispecies civilization of Sol contacting the other Phelan colony systems. The Sails of Tau Ceti, alas, never had any sequels written in such a future. Maybe if there were, I would have been happier with the book.