A fire upon the deep - Vernor Vinge

Thousands of years hence, many races
inhabit a universe where a mind's potential is determined by its
location in space - from superintelligent entities in the Transcend, to
the limited minds of the Unthinking Depths, where only simple creatures
and technology can function. Nobody knows what strange force partitioned
space into these 'zones of thought', but when the warring Straumli
realm use an ancient Transcendent artefact as a weapon, they unwittingly
unleash an awesome power that destroys thousands of worlds and enslaves
all natural and artificial intelligence.
Fleeing the threat, a
family of scientists, including two children, are taken captive by the
Tines - an alien race with a harsh medieval culture - and used as pawns in
a ruthless power struggle. A rescue party, not entirely composed of
humans, must free the children - and retrieve a secret that may save the rest of
interstellar civilization.