Relic

Alan Dean Foster’s Relic is a novel set in the future after humanity has colonized many worlds, continued their penchant for self-destruction, and managed to unleash a plague that killed every member but one, Ruslan.  Ruslan has been pulled from the wreckage of humanity by the Myssari who have been studying him, and the wreckage of human society, ever since.  Eventually Ruslan convinces the Myssari to try to find Earth and the story goes from there.

Straight up SF this book includes not one but two different alien species that the author has great fun developing.  Although there is plenty of action, overall the pace of the book is a bit slow.  I would recommend the book but you might want to skim ahead when you find yourself getting bogged down.