Gwen and Elyan visited their fathers grave accompanied by Gwaine, Percival and Leon. On their way back to Camelot, they were attacked by Snakes and Percival and Leon was bitten. Elaine told Gwen to make a run for it but Morgana was able to capture him. The rest went back to Camelot to have Gauis treat the injured knights. Immediately Gauis recognizes that wounds are not ordinary and Morgana was involve.
Arthur then ordered a rescue party to leave at Dawn. Arthur and Merlin along with other knights set out to search for Gwen. They had to went through an enchanted forest that keeps on tricking them in finding right direction. Finally they were able to get past through using Merlin's magic. Off course Arthur and the other knights are unaware of that Merlin was using Magic.
They were able to reach the Dark Tower where Gwen was being kept captive. All this time Gwen was being tortured by illusions but Gwen was able to resist. As they were about to reach Gwen, they were lead to a room filled with Bobby traps. Elyan was first to get pass through and reached Gwen. Unfortunately another trap is waiting for him. Morgana enchanted a sword to prevent them from saving Gwen. Elyan was able to beat the trap but was mortally wounded in the process.
They returned to Camelot and gave Elyan a knight's burial. At night fall, Gwen slipped out the castle and meet Morgana. It was revealed that Gwen was able to resist the tortured and has become Morgana's ally.
Hopefully Gwen is only under a spell. In the next episode's trailer, Gwen would betray Camelot and Merlin will grow suspicous of Gwen's behaviour. I guess we will have to see how the story unravels.