The Return of the Emperor (Sten #6‪)‬

The Eternal Emperor was dead, and the five members of the Privy Council ruled in his place. But they quickly discovered that their power would collapse around them if they didn't locate the Emperor's secret source of Anti-Matter Two, the economic keystone of the Empire. And so they sent a team of crack commandos to capture Sten, one of their late ruler's few surviving confidantes. But Sten, as usual, had his own agenda. For he knew something about the Eternal Emperor that would shake the Empire to its foundations. And to play his part, all Sten had to do was kill the five most powerful beings in the universe!