Sunreach. Skyward Flight: 1

From #1 bestselling author Brandon Sanderson and Janci Patterson comes the first of three Skyward series novellas, set between Starsight and Cytonic. When a planet-destroying Delver suddenly appears in the sky of Detritus and vanishes just as suddenly, FM knows that the last free human society got lucky. Her Skyward Flight companion Spensa figured out how to draw this Delver away, but it won't be so easy next time.
The forces of the Galactic Superiority will be back-and if the Defiant Defense Force can't figure out a way to escape the planet, humanity's destruction is only a matter of time. Spensa's mission to infiltrate the Superiority unveiled the secret to their hyperdrives-a cytonic slug species called the Taynix. Now FM's flightleader Jorgen has found a large group of Taynix hiding in the caverns far below Detritus's surface.
FM and Jorgen must work together with the engineer Rig to awaken the mysterious alien Alanik and unlock the powers of the Taynix, or humanity will be trapped. With Spensa's friend Minister Cuna of the Superiority stranded at the outpost of Sunreach, they need to figure out how to rescue her-before her foes in the Superiority government can prepare a new weapon to wipe out Detritus once and for all.