I've been meaning to read Labyrinth by Kate Mosse for ages; lots of people told me it was fantastic. I'm not generally a fan of Grail conspiracy theory novels, I find them quite annoying, but as they go, this one was pretty good.

It follows the story of two girls separated by centuries: Alais, who lives in the 1200s in Carcassona; and Alice, who lives in the modern world and is helping her friend on an archaeological dig. Alice stumbles across a hidden chamber in which two bodies are buried with a ring and a small case. A picture of a labyrinth carved into the rock captures Alice's attention, and she sets out to discover the history behind the people and the place. Along the way, she realises people are trying to stop her, and that she's dealing with some very dangerous issues. In the meantime, we follow Alais' quest to preserve her family traditions throughout the war that's gradually moving towards her city.

It's pretty long, but if you have time to spare and nothing else on your bookshelf, it's worth a read.