Silent Star

This is an Apple Books audiobook narrated by a digital voice based on a human narrator.

An unknown alien object (UNOB) is approaching Earth. Coming in dark and silent the object is code named "Silent Star" and the decision is made to intercept the object before it reaches Earth. Captain Linkletter and his team are sent on an intercept course with orders to dock, enter, and assess the threat of the UNOB, and if necessary, destroy it. Linkletter succeeds in entering the UNOB to find it empty but then it comes to life. Essentially a subspace stepping stone, the UNOB is the last step for an invasion force coming to conquer Earth. Surprising the first invaders to reach the UNOB, Linkletter and his squad use the UNOB transporter to hop back up the chain, fighting their way to the UNOB launchers. Quickly they realize that the invaders are an allied force of different alien species. Retreating through the UNOB stepping stones back toward Earth, the last battle is fought in Earth orbit where victory depends on turning alien species against each other.