When Gwen is snatched from Camelot without warning, Merlin knows there can be only one person responsible: Morgana. Arthur is determined to rescue his queen, but it will not be easy; she is locked in the Dark Tower, a place that haunts the dreams of men...

When Merlin agrees to help a young Druid boy, he has no choice but to leave Camelot on a dangerous mission. And with the citadel distracted by the visit of the fearsome Sarrum of Amata, it seems that no one will notice his absence. But as the sky darkens, so do Merlin's suspicions - is there more to Daegal than meets the eye? And can a man as ruthless as the Sarrum ever really be trusted? Too late, the young warlock realises he's made a terrible mistake.