Episode 5 of 13. First transmission on Saturday October 31st, 2009 (UK)
The official details about the episode are as follows…
Uther is delighted when Lady Catrina arrives in Camelot, in the first episode of an exciting two-parter in the magical fantasy drama. Merlin and Gaius, however, suspect that she is not what she seems.
Uther is captivated by his latest guest but Arthur is appalled by his father’s flirting. Merlin is horrified for a different reason – he discovers that Lady Catrina is really a troll but can’t get Arthur to believe him.
Catrina and her strange servant, Jonas, are welcomed into the heart of Camelot and it is up to Merlin to prove that she is a monster and to save Uther from ruin. Unfortunately, Catrina has her sights set on a much greater prize than the King’s heart. Can Merlin overcome her powerful troll magic before it’s too late?
Uther is played by Anthony Head, Lady Catrina by Sarah Parish, Merlin by Colin Morgan, Gaius by Richard Wilson, Arthur by Bradley James and Jonas by Adam Godley.