1x13 - The Legend of Prince Valiant

With Arthur and Guinevere gone, Lady Morgana seizes an opportunity to rid herself of long-time rival Merlin once and for all. She poisons the old wizard with a sleeping potion that traps him in a dream world that she controls. The trio only has a day to save him and seeks help from an eccentric alchemist named ""The Mighty Oom."" Rowanne tests the antidote he gives them and falls seriously ill, which forces her two friends to confront their feelings for her.