From audible.com:

The year is 3326. Nigel Sheldon, one of the founders of the Commonwealth, receives a visit from the Raiel - self-appointed guardians of the Void, the enigmatic construct at the core of the galaxy that threatens the existence of all that lives. The Raiel convince Nigel to participate in a desperate scheme to infiltrate the Void. Once inside, Nigel discovers that humans are not the only life-forms to have been sucked into the Void. The humans trapped there are afflicted by an alien species of biological mimics - the Fallers - that are intelligent but merciless killers. Yet these same aliens may hold the key to destroying the threat of the Void forever - if Nigel can uncover their secrets.