The Dark Arena was his first book and it's a World War II book. The main character, Walter Mosca was in the war, and returns home to America when it's over. But he met a girl over in Germany and goes back in search of her. That's just a very basic outline, worth checking out. It's not really a love story like I've just made it sound, but it's different from all of Puzo's other books I thought.
His second novel was The Fortunate Pilgrim, about an Italian immigrant family. The plot isn't the easiest to explain without giving things away, but it tells of a family and their struggles in America.
Puzo's third book was The Godfather, which I don't think I need to go into detail on.
I hope I helped you there, Domenico.