That flaw is that Brown's view of Jesus is based on two indefensible assumptions. First, Brown assumes that the early church never thought of Jesus as divine. As noted above, Brown believes that Jesus' divinity was never seriously asserted until A.D. 325 at the Council of Nicea (the council that produced the famous Nicene Creed). This, of course, is demonstrably false. Paul's letters were written between A.D. 49-65, and are filled with references to the deity of Christ, a doctrine obviously believed by him and his readers (cf. Col. 2:9; Phil. 2:6-11). Also, John's gospel, written no later than A.D. 95, emphatically declares, "In the beginning was the Word, and the Word was with God, and the Word was God" (John 1:1). Even Matthew, Mark, and Luke, arguably first-century works, strongly underscore the divinity of Jesus. Moreover, Pliny the Younger, the early-second century philosopher, notes that Jesus' disciples revered him as "a god." Belief in the deity of Christ, therefore, can be found in the earliest available sources, long before the Council of Nicea.
Second, Brown falsely assumes that the New Testament Gospels are late and unreliable as historical sources. Like the infamous Jesus Seminar, he chooses to place greater trust in certain Gnostic works like the Gospel of Thomas. However, as noted above, the New Testament Gospels are early sources. It can be demonstrated with high confidence that Matthew, Mark, and Luke pre-date Paul's martyrdom in A.D. 65. Notice, for example, that the book of Acts ends with Paul still awaiting his trial before Caesar which place c. A.D. 62. This suggests that Acts was written before the trial. And this means that Luke's Gospel had to have been written about the same time as Luke. And since Matthew and Luke likely borrowed material from Mark, it is virtually certain that Mark was written in the early A.D. 50s. The Gnostic Gospel of Thomas was written no earlier than A.D. 150. The claim that it contains more accurate historical data about Jesus than the biblical Gospels is ludicrous.
Steven B. Cowan's short review of Dan Brown's The Da Vinci Code can be found in the July-August 2004 edition of the Areopagus Journal (published by the Apologetics Resource Center)