A year has passed since Morgana fell from power and openly betrayed Camelot, and Camelot has entered a dark age. With Uther left heartbroken from the ultimate betrayal his daughter committed, it is now up to Prince Arthur to take charge. A new face has arrived at court; Agravaine, the young Prince's uncle and most trusted advisor, however is he to be trusted? After all one can be betrayed by anyone, Arthur has been forced to learn. With Morgana's powers growing at an alarming rate outside the castle walls, Merlin must be more cautious than ever if he is to protect Arthur and save Albion from falling into dust. With the trust of Merlin, Guinevere and Gaius to back him as Camelot enters dark times, Arthur is given a lease of hope. However whilst enemies grow stronger outside the walls of Camelot, another flourishes from within....with loyalties tested to their very limit, Merlin and Arthur must place their full trust in one another if they are to prevent the kingdom from falling into Morgana's hands; if the vengeful sorceress takes the throne, Camelot will be doomed to eternal darkness. As Morgana spreads fear and horror throughout Albion, Guienevere meets her destiny, Arthur finds the weight of a kingdom to bear and Merlin finds his destiny fast approaching, the battle for Camelot may be closer than anyone could've thought....
The production of a fourth series of Merlin was confirmed on 25 October 2010. Anthony Head confirmed that the show will air in September 2011. Series 4 will consist of 13 episodes. Colin Morgan said episodes would no longer be as stand-alone, "Each episode takes a progression as a piece of a jigsaw that has to be completed. There's no reverse going on." Due to the popularity of the show, Merlin has been renewed for a fifth series.
Casting
Three days before the series finale Julian Jones the series creator stated that Colin Morgan, Bradley James, Katie McGrath, Angel Coulby, Anthony Head, and Richard Wilson are all contracted for multiple season and they would return as series regulars. John Hurt who narrated the show and plays the voice of the great dragon would also be upgraded back into a series regular after having a recurring role in season two. On 19 August 2011 Phil Davis was cast as the Gleeman. Nathaniel Parker and Charlene McKenna would also join the casting playing Agravaine and Lamia. James Callis joined that casting for the fourth episode as Julius Borden. Gemma Jones will play Cailleach the gatekeeper to the spirit world. Lindsay Duncan will appear in one episode playing the Queen of Annis. Steven Hartley also joined the casting as King Caerleon. Rupert Young will also return. Tom Hopper and Adetomiwa Edun confirmed that they will also return on their roles.
