This book is both a psychological study of the break-up of a marriage and an action-thriller. Jay Finch is a spy and a teacher in Botswana but what he really wants to do is write poetry. Rush captures the feelings and conversations between husband and wife, a thousand changes of mood and feelings within each conversation.
The 'action' in the middle of the book moves it along well enough, and while there are some crazy scenes, it weakens the plot. Jay becomes more of himself - neurotic and paranoid - which threatens both his safety and sanity. He says that he knows he shouldn't do something - and goes ahead and does it. Maybe that's how "Mortals" is different from other spy books, where the agent stuffs his true feelings and gets on with his work. Jay is a bumbling agent, who discovers that he's disgusted with the work he's asked to do.
The book is also about redemption, though the last section doesn't quite fit with the picture of Jay that evolves during the book.
Rush's writing is inspired in many places. He captures the contradictions of being an expat in a foreign place, of being in a country but separate from the culture. Some of it is just too long, and I gloss over many of the sections of tormented internal ramblings.