If you want a few hundred words on a full plot summary read the wikipedia page on the story.
Written some ten years after the young Linebarger wrote ‘Scanners Live in Vain’ (it took five years to get that story published), this story is similarly set in a future with ‘The Instrumentality’ and has mention of ‘Scanners’. But here the story revolves around telepaths, without whom humanity cannot travels outside of our solar system. There are dark energies out there, which we perceive as dragons, and these telepaths (‘pinlighters’) with their companion ‘Partners’ do battle with these enemies.
The story has many excellent turns of phrase, and leads the reader through the story introducing background concepts and technology, with the odd clever ‘reveal’ (we aren’t told immediately that the small ‘Partners’ are in fact cats).
The dark depths of empty space are well captured, as is the combat and the psychological issues (these latter being Linebarger’s military specialism), and with a neat touch of humanity at the end (the protagonist finds that no woman can compare to his companion feline).