I think a bit more on the person's background, e.g. familiar with real Christianity, Orthodoxy or not, would be helpful for a sound recommendation.
That said, I still think C.S. Lewis' works like the Screwtape Letters, Mere Christianity, Problem of Pain, and the Great Divorce (all can be found in one book) present a helpful, generic Christian perspective. Is it high theology? Certainly not, but I get the feeling that people who demand exhaustively rigorous theology to shore up their faith may be in trouble.
St. Athanasius' On The Incarnation may be helpful.
Looking forward to additional suggestions.