Fleeing enemies, Merlin and Arthur take refuge in The Valley of the Fallen Kings. There, the sorcerer Taliesin cures the wounded Arthur and shows Merlin the Crystal Cave, which provides a disturbing vision of the future in which Morgana stabs a sleeping Uther. Come her birthday, Morgana, given a dagger by Arthur, steals into the king's room to kill, secretly followed by Merlin, who uses magic to thwart her. She is temporarily put into a coma, during which time Uther confides in Gaius that she is his natural daughter - a fact of which she is also aware. Gaius believes that Arthur should be told as now Morgana is a legitimate heir to throne and he stands in her way.
—don @ minifie-1