Author Dan Brown conceded on Wednesday that some of the ideas he took from two historians who accuse him of plagiarism were essential to ``The Da Vinci Code,'' but said the bestseller had many other important themes too.

On his third and final day in the witness box, the 41-year-old expressed frustration during a grueling session of cross-examination in the closely-watched copyright case at London's High Court.

Michael Baigent and Richard Leigh wrote a 1982 book of historical conjecture called ``The Holy Blood and the Holy Grail,'' which they claim Brown lifted wholesale for his novel.

Random House argues that neither Brown nor his wife Blythe had read the 1982 Holy Blood book by the time he composed the synopsis for The Da Vinci Code in January, 2001.

Justice Peter Smith sought to clarify the point, asking the claimants' lawyer, Jonathan Rayner James: ``Do you accept Mr. Brown's evidence as to when he said he first saw Holy Blood, Holy Grail?''

Rayner James replied: ``Mr. Brown denies it. We say his wife had it by that time.''