I can stop it, he thought, the heartbeat of the cave pulsing in his ears. I have seen the threads; I can cut them.
This request refers to the fifth episode of the third series of the BBC show , titled " The Crystal Cave ". In this episode, the young warlock Merlin is shown a glimpse of the future by the sorcerer Taliesin, leading to a series of events where Merlin’s attempts to change fate inadvertently bring it to pass. [S3E5] The Crystal Cave
Merlin remains the silent guardian, standing in the courtyard as the sun sets over the citadel, knowing now that some paths are carved in stone, and even magic cannot wash them away. I can stop it, he thought, the heartbeat