Over the Wall: A Warrior Druid of Britain Novelette

Beltane, AD425
Northern Britain
Midnight approaches and in Dun Breatann's great hall the Beltane feasting continues, with stories and songs and as much meat and ale as anyone could wish for.
On the western side of the towering fortress however, ten small figures make their way up the shadowy rock. Armed to the teeth, and hand-picked for their particular, deadly skills, these warriors have travelled far across the sea from Dalriada and are utterly focused on their mission, despite the fact most - perhaps all - of them will die this night.
High above, guards patrol the fortress walls as usual, but they expect yet another quiet shift for, as everyone knows, Dun Breatann is impregnable.
Isn't it?