Legacy of the Centaur

In the 8th book in the Reckless Faith series, the crew of the Faith and their allies are tasked with rescuing the sibling of an old friend, who has been imprisoned on a distant planet for a crime he didn't commit. They soon discover that the prison is far underground, protected by both a hostile fleet and a hellish atmosphere, and holds secrets beyond anything they could have imagined. Pushed to their limits, the team must call upon all of their experience and resources to find the sibling, and uncover the truth about the subterranean prison known as Inferno.