Let’s say you are good friends with a devout baptist (could be any Protestant, really, but I use baptist because it is a more radical sort of Protestantism). He is well-read in the Scriptures, has a strong relationship with the Lord, and is super-intelligent (has an IQ of 160). He knows you are Catholic, but when you talk with him about the Catholic faith, he counters your beliefs with a barrage of his own systematic knowledge of revelation. He seems not even to seriously consider your Catholic beilefs. One day he finally agrees that he will read any Catholic book you choose for him to read, so long as you read a Protestant book of his choosing in return. He says that he will consider your book choice as seriously as he can, but that if he discovers the book to be poorly argued, he will not read any more Catholic books.
Now, if you were in this situation and could rely on only one book to latch him onto Catholic truths, which book would you recommend?
By the way, the Protestant profile listed above actually fits a few of my friends, but I ask this question not in reference to them but because I am interested in which book best presents the truth of Catholicism and challenges even the best reasoned Protestant claims.