On an intergalactic spaceship, two runaway servants turned mercenaries agree to a dangerous mission that will take them back to the planet from which they escaped—in return for a shot at a clean record and a peaceful life.

When a posthuman 'hardshell' robot finds an injured biological human who has committed war crimes against hardshells, the hardshell's programming will not allow it to let the human come to harm, so it must use all the resources it has to find a way to bring this war criminal to justice.