Orion Arm: The Rampart Worlds: Book 2 by Julian May
A gripping sf adventure from the acclaimed author of The Pliocene Exile series.
Two hundred years into the future, the great corporations of Earth dominate all life in our Galaxy. But their endless pursuit of wealth and power is about to open the door to a malevolent alien race, intent on engulfing the commonwealth of Human Worlds.
Helly and his companions attempt to capture a crucial witness to the Galapharma conspiracy, who has taken refuge on a hostile planet. Its insanely ambitious boss, Alistair Drummond, will stop at nothing in his quest for power, and Helly is marked for death as the two corporations continue to do battle.
Meanwhile, the Haluk follow their own appalling agenda, using human science to mutate their bodies, allowing them to infiltrate human society. Helly must find a way to alert the Human Commonwealth to the Haluk peril, while also saving his family from Drummond's increasingly desperate efforts to annhilate the Rampart worlds.