Something's shooting down shuttles when they try to land on the surface of Pluto.
After an invisible force annihilates two shuttlecraft in rapid succession, the humans at Pluto Station find themselves pitted against a weapon they can't see. Every time it fires, the weapon gets stronger, until it's targeting anything heading in-system. Meanwhile, their resupply freighter is on approach, carrying all their food and equipment for the next three months. Its destruction will mean starvation.
The only humans on our solar system's outer rim have just days to identify whatever hangs in the space between Pluto and Charon-and then either disable it, or else destroy it.
