While visiting her father’s grave, Gwen is separated from her protector knights and brother Elyan when she is set upon by a nest of snakes, the work of Morgana’s dark magic.
While the knights return to Camelot without their mistress, Morgana takes Gwen to the fabled Dark Tower, much feared by the knights, and locks the young queen in a darkened room.
Arthur, Elyan, Merlin and some knights set out to save the damsel in distress. Meanwhile, Morgana plays twisted mind-games on Gwen in a bid to send her mad.
While trying to break through an impenetrable forest, the spirit of the forest, Queen Mab, reveals herself to Merlin and helps him find the right way to the tower – but warns him that one of their party will not return home.
Inside the tower, the rescuers face a series of deadly traps, including an enchanted sword destined for Arthur. Wanting to be brave, Elyan clashes with the sword, which he defeats thus saving Gwen, but is fatally wounded in the process.
The episode ends with Elyan’s funeral and a now brainwashed Gwen meeting Morgana in secret who tells her that together they will bring forth Arthur’s destruction.