Marrow is set on 'The Ship', a massive (and I mean massive) starship/space station discovered and inhabited by millions of immortal humanoid, alien and artificial (AI) lifeforms. No one knows who built The Ship or why it was built but everyone lives on it in relative harmony. The tale centres around the 'Captains' - the ship's police force / crew. Originally, everyone thought that The Ship had been fully mapped but when a tunnel leading to the centre of The Ship is discovered, a team of the best Captains are sent to investigate and they find something that totally changes their lives and those of the billions of inhabitants of The Ship. The story spans millennia as people live for centuries and The Ship travels through the Galaxy and beyond. It is well written and the characters have the depth to make you care about them. Fans of Iain M. Bank's Culture novels will enjoy Marrow as both writers use hedonistic societies based on high technology. Excellent.