Fall of The Messengers

When =ca.85 arrives on Earth and takes human form, he is mysteriously separated from Frisa, his companion and co-messenger. Humanity and the remnants of civilization trudge on in the aftermath of a nuclear war, desperately in need of the message he and Frisa came to deliver. But =ca.85 has never been alone before, and after stumbling on the scene of a murder, there are soon multiple mysteries to solve. Taking on the identity of a detective, Planchette, he must find Frisa, catch a murderer, identify the recipient of his message, and ultimately unravel the enigma of his own being. He has lived many lifetimes on many worlds, but these mysteries are all connected, and there is more at stake than even the fate of Earth and humanity.