The age of interstellar exploration, humankind at war (now isn't that typical ? :-). The enemies are regul, beings with long life and an absolute memory - only regul consider themselves too precious to get involved in fighting, sending mri mercenaries to fight in their stead.

Regul are loosing the war, and being a calculating race, they decide to negotiate with humans, sacrificing mri lives to stall their advance and to gain as much ground as possible in the oncoming negotiations. But regul overdo this a bit and manage to wipe out almost the entire race of mri, leaving only two survivors (of course, this is not entirely unfortunate for regul, who fear mri taking service with humans).

The two surviving mri indeed end up in the hands of humans. Being the only mri ever to be captured alive, they become a scientific curiosity - hated by most of their captors who remember the blood spilled during the war, but also regarded with growing anxiety, for killing them means terminating a sapient race - something nobody really wants on their conscience.

As it turns out, the two mri carry with them a navigation chart, possibly plotting a way to the homeworld of mri (until then, its existence was only suspected by humans, and arrogantly overlooked by regul). The problem is, what to do with it ?