Imagine if you will, a race as interconnected as the cells of your body. Trillions of beings, their shapes as different as you could imagine in your wildest, feverish dreams, all striving for one purpose. Millions can (and will) sacrifice themselves for the greater good.
What said purpose or greater good are, we can only guess at.
The Ravagers came out of nowhere a few decades ago, and almost at a whim, destroyed two planets without much hassle.
No. Not destroyed. Consumed. Ate.
These cosmic locusts descended upon Izuan Tai and Persaius and reduced all organic material to goo. And then fed this goo to their ships in orbit.
The Corvo and Iz'kal navies managed to get some revenge on these dead worlds, and that, was assumed, was that. The Ravagers retreated into the depths of the Labyrinth, usually reduced to minor skirmishes or strategic attacks.
The truth, however....
The Ravagers are evolving. They are probing the defences of Known Space. Their Harvesters are absorbing victims and learning about them. Their Ironskins are eating the Known Races' metals and instinctively understanding their alloys, their weaknesses.
Soon, the Queens will know much more about Known Space than they did. Information is ammunition, they say. Soon, they will make a move.
And may The Five Gods help us when they do, because there will be no one left.