This new novel by Rebecca Goldstein, whose Strange Attractors is one of my favorite works of mathematical fiction, features as two main characters a woman known as "the goddess of game theory" and a Hasidic sixyearold mathematical genius. According to the cover:
(quoted from 36 Arguments for the Existence of God)
At the center: Cass Seltzer, a professor of psychology whose book, The Varieties of Religious Illusion, has become a surprise best seller. He's been dubbed “the atheist with a soul,” and his sudden celebrity has upended his life. He wins over the stunning Lucinda Mandelbaum—“the goddess of game theory”—and loses himself in a spiritually expansive infatuation. A former girlfriend appears: an anthropologist who invites him to join in her quest for immortality through biochemistry. But he is haunted by reminders of the two people who ignited his passion to understand religion: his teacher Jonas Elijah Klapper, a renowned literary scholar with a suspicious obsession with messianism, and an angelic sixyearold mathematical genius, heir to the leadership of an exotic Hasidic sect. The rush of events in a single dramatic week plays out Cass's conviction that the religious impulse spills out into life at large.

Of course, as the title suggests, the main focus of the novel is a sort of exploration of reasons to believe in God. The titles of the chapters have cute names like "The Argument from Dappled Things" and (more mathematically) "The Argument from Prime Numbers". However, one should not look to this book for serious arguments for the existence of a supreme being. In fact, the appendix to the book enumerates the flaws in each of the arguments, which might itself seem like an argument in the opposite direction. In the end, rather than being about logical arguments why people should believe, it is more of an emotional investigation of why they want to.
Still, there is enough math here to include the book on this list. It comes in the form of matrices of the sort that game theorists like to make, but here applied to the question of whether the two partners in a romance should say "I love you". (Unlike some lame mathematical romance of the form "you + me = love" that one sees in other mathematical fiction, this actually is a reasonable even if unorthodox application, with s surprise twist ending.) Another source of math in the book is the young son of a rabbi who has great insights into the properties of the natural numbers (e.g. primes, squares, factorials, and their relationships) despite lacking any formal training. This prodigy reenters the story at age 16 when a famous mathematician meets with him to convince him to attend MIT. Finally, another woman in Cass' life is a poet named Pascale whose father is a mathematician in France. Ironically, she is named after Blaise Pascal, but does not believe in probability theory. (She insists that any event has a probability of either zero or infinity!) 