Call them the Strangers. Like most solar systems, beyond the worlds favored by the pre-dead and the failed sun worlds, there was an asteroid belt. This is where they came, to build, to wait, to eventually send ships out to new systems. Sooner or later, they would encounter the pre-dead as they had in this system. After the first pre-dead survey ship had left, construction began, pausing only when pre-dead starships were in the system. Giant lasers focused on a suitable asteroid. They cooked it, melted it into a solid lump instead of a pile of rubble. They added reinforcing material, cavities were excavated, and they allowed the former asteroid to cool, to solidify. Weapons, an anti-matter drive, and a controlling computer were incorporated into the once-harmless piece of space debris. Mirror armor coated its entire surface to be covered in turn by a layer of rubble. Finally, indistinguishable from any of hundreds of other space objects, they placed the drone in an orbit that would, once every seven years, bring it near the planet which the pre-dead wanted for their own.

The orbit was not too close to the planet, yet not too far away.

It would not do for the pre-dead to think this harmless floating rock needed to be moved, destroyed lest it hit their planet.

The pre-dead should suspect nothing until far too late.

Even though, unlike the pre-dead, they had all the time in the Universe, they did not want to wait seven years to trigger their trap.

So the Strangers made more, many more drones. One would always be no more than a month or so distant from the target world.

This was an old trick. It had always worked before.