Months after Stalliongrad joined forces with Equestria to push back against the Changelings, Captain Winter Loch and his crew are sailing north alongside a fleet of other submarines to prevent Changeling Convoy's from supplying their forces in the land war.
In an ironic twist, they encounter a Changeling Raiding Fleet attacking an Equestrian Convoy and rush to their aid.

Captain Winter will bring his crew as deep into Tartarus as he must to ensure the safety of his Equestrian Allies.
And if he and his crew survive? There's no better time to celebrate living than under the shining Summer sun.