The Legend of Prince Valiant

The Eyes of the Serpent (2x27)

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A recurring nightmare involving a golden serpent has the prince worried about his future and the safety of Camelot. Merlin tries to reassure him that some dreams are just dreams and sends him on a mission to see The Mighty Oom. While there, Valiant's dream grows more vivid and deadly - he can feel that something bad is coming. What eventually does come threatens Camelot as well as a lovely young woman Valiant meets.