Story details for the fourth episode of Merlin Series 5 have been revealed.

With Princess Mithian as the perfect bait, Morgana conjures a deception so powerful that the whole of Camelot is taken in – even Merlin himself. But as the storm clouds gather, will the young warlock see through the lies? Or will Morgana at long last fulfil her dreams of revenge?

Colin Morgan is Merlin, Bradley James is Arthur, Angel Coulby is Gwen, Katie McGrath is Morgana, Richard Wilson is Gaius and John Hurt as the voice of the Great Dragon. Tom Hopper, Rupert Young, Eoin Macken and Adetomiwa Edun returns as The Knights of the Round Table. Special guest stars include Janet Montgomery as Princess Mithian, James Fox as King Rodor and Fintan McKeown as Odin.

Episode 4 airs Saturday 27 October 2012 at 8.20pm on BBC1.