The Changeling Kingdom has fallen. Queen Chrysalis has been captured and the hive has reformed under King Thorax. Victory is now firmly in the Equestrian's hooves.

But lurking underneath the waves of Equestrian waters, is one of the most advanced stealth weapons in history. A vessel capable of silently sinking whole fleets of ships and disappearing without a trace. And crewed by changelings so loyal, they would rather go through Tartarus and back then reform and betray the Queen.

The only thing is, they don't know the war is over...

This story was inspired by the movies Hunt for Red October, Greyhound and Hunter-Killer, as well as submarine games Harpoon, Dangerous Waters, Cold Waters and the Silent Hunter series.