Blade of Fortriu

The kingdom of Fortriu has enjoyed five years of peace since Bridei came to the throne. Now the king is preparing for the long-awaited war that he hopes will see the Gaelic invaders driven from the west forever. The princess Ana, a hostage of Fortriu since childhood, is sent north to make a strategic marriage with a chieftain she has never met – and with it gain an ally on whom Bridei's victory relies. Her escort is led by a man she despises: the enigmatic Faolan, Bridei's assassin and spy.
The expedition is ill-fated, and when Ana arrives at the chieftain Alpin's stronghold in the mysterious Briar Wood, she is uneasy. This is a place full of secrets. When Ana discovers a prisoner kept within the bleakest of confinement, she is met with a conspiracy of silence. Faolan, tortured by an impossible love, walks a delicate path between loyalty and betrayal. . .
'Juliet Marillier is among the most skilled of fantasy writers' Sara Douglass