Farthinghome — Nina M. Osier

With their home-world taken over and poisoned, and their navy destroyed, the surviving Humans of the Farthinghome system must choose between setting off into the unknown or attempting to keep their off-planet colonies functioning. Those who cast their lot with the refugee fleet will depend on one man, Father Bazel daKiev, to reach deep into ancestral memories for the coordinates of another world where Humans can live. Meanwhile, the invaders are targeting Humankind's allies -- and at least one of those allies sees in the nearly helpless Humans a target far to inviting to resist.