From New York Times bestseller and master of speculative fiction Garth Nix comes his first foray into adult science fiction with a brilliant and poignant stand-alone story of sentient starships, galactic warfare, and the bonds a crew forms far, far from Earth.

Caught me a mountain
Rode it to the stars

It's business as usual for Ship Leader Parnell Shi-Sawahla and the crew of the corvette Sassafras. Ride a Massif to a new system, fight the enemy, repeat. For more than two hundred years humans have been hitching rides on these sentient, starfaring mountain ranges, colonizing planets and exporting an on and off again war between Earth and Mars.

But the big questions are always there, behind every battle, every new colony, every new star system discovery.

Why do the Massifs carry humans to the stars?

Why do they help us export our wars?

What's in it for the Massifs?

Ship crews aren't supposed to ask these questions, they aren't supposed to think about these questions, and they definitely aren't supposed to go deep and talk to Massif avatars. But now Parnell and his tight-knit crew must try to find the answers, to save not only themselves but the future of humanity.