Saturn's children - Charles Stross

Freya Nakamachi-47 has some major existential issues. She's the perfect concubine, designed to please her human masters - hardwired to become aroused at the mere sight of a human male. There's just one problem: she came off the production line a year after the human species went extinct. Whatever else she may be, Freya Nakamachi-47 is gloriously obsolete. What's more, the rigid social hierarchy that has risen in the 200 years since the last human died, places beings such as Freya very near the bottom. So when she has a run-in on Venus with a murderous aristocrat, she needs passage off-world in a hurry - and can't be too fussy about how she pays her way.

But if Venus was a frying pan, Mercury is the fire - and soon she's going to be running for her life. Because the job she's taken as a courier has drawn her to the attention of powerful and dangerous people, and they don't just want the package she's carrying. They want her soul ...