Merlin: The Labyrinth of Gedref

While on a hunting trip with Merlin, Arthur kills a unicorn and Merlin sees an old man watching from afar. Their eyes meet and the old man quickly disappears. Meanwhile, Camelot's crops have died mysteriously, and its water has turned into sand, sending panic and frenzy throughout the kingdom. Gaius believes that the unfortunate events cannot be a coincidence and a curse has been placed on Camelot. Later, while Arthur and Merlin are on patrol, they come across the same old man Merlin had previously seen. He introduces himself as Anhora, keeper of the unicorns, explaining that Arthur is to blame for all the current misfortune in Camelot because he slayed the unicorn. The only way Arthur will be able to save his kingdom is through a series of tests.