Readers familiar with Change of Command will notice a temporal overlap between the last part of that book, and the first part of this one. Here the first chapter starts between the mutiny and the second assassination.
Newcomers may wish a bit more background.
The Familias Regnant is a political assembly of great families, now spread across hundreds of solar systems. Centuries ago, they combined their individual family militias into the Regular Space Service, which has the dual mission of policing the spaceways and defending the Familias from external attack.
In the previous book, Change of Command, longstanding dissension and unrest in the R.S.S. came to a head and elements of the Fleet mutinied.
The mutineers first struck at the Fleet training planet, Copper Mountain, freeing some of the prisoners from a high-security brig on a remote island. The rest they massacred. Their original plan had included taking over a weapons research facility, but loyalists managed to prevent that, at least for the moment. Unfortunately, the mutineers managed to destroy their transportation: the loyalists are marooned.