A lawyer for the publisher of blockbuster thriller “The Da Vinci Code” chipped away Thursday at the claims of two authors who allege copyright infringement, forcing one of them to concede that a key plank of the case is wrong.

Michael Baigent and his co-author Richard Leigh are suing Random House at Britain’s High Court over the copyright of their 1982 book, “The Holy Blood and the Holy Grail.” They claim Dan Brown’s best seller “appropriated the architecture” of their work, which explores theories that Jesus married Mary Magdalene, the couple had a child and the bloodline survives.