Introduction and disclaimer: The characters in this story are either the creations of those involved in the production of Star Trek over the years or are the author's interpretation of what characters created by those involved in Star Trek might be like in a mirror universe. With respect to a couple of characters there are similarities to those created in a comic book story, but they are not the same people. For the purpose of this story I'm assuming that while Spock did become the Empire's Commander-in-Chief he was overthrown by the Imperial Starfleet shortly thereafter. For information on the comic book search for "mirror universe saga" at Amazon or Barnes & Noble. No copyright infringement is intended.
No one was more surprised than Smiley by the Klingon who chose to fight alongside them. The aged Klingon commandeered a Bird-of-Prey shortly after Terok Nor's capture by the rebels and took it to the station where he surrendered to make his offer. When asked why he said it was to restore another's honor.
A common enough reason for a Klingon to fight, but fight alongside Terrans? Kruge's age made it all the more puzzling. O'Brien estimated he had to be at least a century—old enough to remember when his own people were the ones enslaved by the Terran Empire. If anything this Klingon would wish to destroy the Terrans more than anyone. This was one reason O'Brien was skeptical. Bashir trusted him even less.
"Whose honor?" O'Brien asked.
The Klingon hesitated before responding. "A Terran's honor. Someone you seem to be very much like. If I fight alongside you I will have a chance to fight a battle in his name."
"I think I have an idea," Dax broke in. "If it's whom I think it is I knew him as Curzon," she said. Kruge looked at her for a second. Dax continued. "It's David Marcus, isn't it? You want to help him enter Sto-vo-kor, don't you?"
Kruge nodded. O'Brien was stunned. Bashir started to grab the old Klingon but Dax held him back. O'Brien looked at both Dax and Kruge. "Perhaps one of you could explain," he said.
"The official Alliance line is that Marcus betrayed his own people to us. It maintains this lie as an example of Terran lack of honor," Kruge replied. "Marcus was an honorable warrior. He deserved better than to be dishonored by those he fought for."
Dax continued. "Marcus helped the Klingons resist Terran occupation, that's all. He never intended for them to turn around and conquer Earth. He didn't expect they'd even be able to.
"Marcus' mother was executed by the Empire. They knew about the first crossover and how it affected Spock and some others. Carol Marcus was one of those they won over because she realized how different David's father had turned out on the other side. When Spock was overthrown David sought to carry on his vision of reform through an underground movement. When the Klingons were conquered he worked with them. He didn't count on Cardassia's involvement."
"That was something no one had expected," Tuvok said. "At the time Cardassia wasn't considered as powerful as either the Terran or Klingon empires. When Cardassia entered the war we did not realize they were purchasing dilithium from an unknown race."
The Ferengi, Smiley realized. Because of those shipments Cardassia made enough gains into Terran space to hook up with the Klingons.
"And once Cardassia hooked up with us it was a whole new war," Kruge said. "Where Marcus was able to offer hand weapons and scout ships the Cardassians supplied warships. It was a chance to turn the tables and avenge our earlier defeat at the hands of the Terrans. Unfortunately Marcus suffered the consequences."
"And now you want to try to restore Marcus' honor," O'Brien acknowledged.
Kruge nodded. "And earn him a chance to enter Sto-vo-kor as the warrior he was. The chance that he should have had in the first place."
"What became of him?" one of the rebels asked.
"He couldn't live with the knowledge of what he'd helped bring about," Dax said sadly. "He committed suicide."