Promising mortal revenge on Uther, Morgause enlists Morgana's help to spread a sleep plague throughout Camelot, which Gaius can't cure or resist himself. Only Arthur and Merlin haven't succumbed to it, having been on a far mission. As they only survived, none of their knight guards, the attempt to eliminate the ancient undead Knights of Mehdir, which Morgause revived taking the place of their creator-witch, it seems a desperate task to defend Camelot or at least save Uther alone, even if they can stay awake. Merlin seeks the dragon's counsel, and this time swears by his ma's life to free it in exchange. He keeps his word, although the advice was to eliminate the knights' magical power source - witch Morgana.
—KGF Vissers