Apparently the fallen have 'fallen from grace' and seemed to be a once great empire.
Which sounds a lot like what happened to the humans; what if the fallen empire had been hit by the darkness (5th race, pyramid ships .etc), and are trying to get to the traveller to revitalise their old homeworlds?
In which case I will feel really bad for killing em :(
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Kill everyone of them, they're taking up to much space in our solar system.