January 798 UC: A squadron of the Iserlohn Garrison Fleet under the command of Dusty Attenborough conducts a patrol and training mission in the Galactic Empire side of the Iserlohn Corridor, during which it encounters an Imperial patrol fleet under the command of Eihendorf. Hostilities ensue and Attenborough's squadron, largely comprised of trainees, is quickly forced into the defensive. Julian Mintz, one of the trainees, undergoes his first battle as a fighter pilot. The outmatched Attenborough Squadron is on the brink of defeat when it is saved by the entirety of the Iserlohn Garrison Fleet led by Yang Wen-li.

Wolfgang Mittermeyer and Oskar von Reuenthal, two renowned admirals under the command of Reinhard von Lohengramm collectively dubbed as the "Twin Pillars", get together and reminisce about their respective pasts, culminating in the event that would lead to the defining moment of their careers: the Klopstock Incident. In March 795 UC, after thirty years of life in exile from Imperial high society, Marquis Wilhelm von Klopstock plotted an assassination of Kaiser Friedrich IV that was to occur during a party organised by Duke Otho von Braunschweig.

Oskar von Reuenthal ran out in a stormy night to seek help from Reinhard von Lohengramm (then Müsel), a rising star in the Imperial Navy that was also known to be disdained by the high nobles. During the meeting with Reinhard and Siegfried Kircheis, Reuenthal convinced Reinhard to save Wolfgang Mittermeyer, in exchange for the absolute loyalties of both of them to Reinhard. Mittermeyer was promptly freed from captivity, and together with Reuenthal, became the first people outside Kircheis to join Reinhard's cause.

Back in the present, Reinhard is busy consolidating his authority as supreme commander of the Imperial Navy and prime minister of the Galactic Empire, and to facilitate that he expands the number of commanders under his direct command.

As if to fill the void caused by the death of Siegfried Kircheis, Reinhard von Lohengramm devotes his energies entirely on reforming the Galactic Empire. His wide-ranging reforms earn him tremendous goodwill from the populace, and despite considering them to be publicity stunts, even his sceptics are suitably impressed by the breadth of the reforms.

The head of the Galactic Empire's Science and Technology Department, Anton Hilmer von Schaft, is a man known for his sheer ambition. He is now presenting to Reinhard a large-scale plan to retake the long-lost Iserlohn Fortress.

The Empire moves forward with its experiments to warp Geiersburg Fortress through space to attack Iserlohn Fortress. Reinhard and several of his subordinates watch anxiously from the safety of his flagship as the countdown begins. Amidst the tension, some of Reinhard's most trusted men discuss how he has changed since Kircheis died a year ago.

A sudden recall order from the central government of the Free Planets Alliance forces Yang to head for the capital planet Heinessen. Yang assigns the command of the Iserlohn Fortress to Caselnes and von Schönkopf, and departs aboard the cruiser Leda II with minimal personnel, including his second-in-command Frederica and his guard, Machungo.

When the massive Geiersburg Fortress suddenly materializes in the Iserlohn Corridor, Caselnes immediately forwards a request for reinforcements to Heinessen, but now he must prepare for the imminent Imperial attack. Meanwhile, in Heinessen, Frederica is desperately looking for allies to save Yang.

Admiral Kempff, Commander-in-Chief of the Geiersburg Imperial expeditionary force, sends a peremptory declaration of war to the Alliance garrison of Iserlohn. Then Geiersburg's main gun suddenly opens fire with devastating results. On Iserlohn, a confused Caselnes and his officers do not seem to agree on the best strategy to take...

The Imperial fleet relentlessly conducts their assault on the Iserlohn Corridor, one blow after another. As Caselnes is still struggling with organizing an effective resistance, Imperial armored infantry units have landed on Iserlohn, and threaten to establish a bridgehead. Then, former Imperial admiral Merkatz, who defected to the Alliance, asks to be assigned temporary command of the garrison fleet.

An Alliance relief fleet is finally heading to the Iserlohn Corridor, but combat forces on the battlefield are limited, and a wrong move could turn fatal. Should the Iserlohn garrison fleet be unable to break the blockade imposed by Kempff's ships, the reinforcements from Heinessen would be easily destroyed. On the command bridge of Iserlohn, Caselnes and his officers animatedly discuss the countermeasures, but what sounds like the best plan comes from somebody most unexpected.