On the eve of the arrival of a powerful potential ally for Arthur at Camelot, a young druid boy - Daegal (Alfie Stewart) - breaks into the castle seeking to take Merlin to his encampment where his young sister is dying of the sweating sickness.
Little does Merlin realise he is walking into a deadly trap.
Meanwhile Gwen - at the behest of Morgana - convinces the new arrival at Camelot, the evil and sadistic ruler known as The Sarrum (John Shrapnel), to have Arthur assassinated so she can seize the throne.
He, in turn, believes this will be an opportunity to steal the throne for himself "from a servant girl, playing at being Queen".
Sadly, The Hollow Queen is a very flawed episode at the most basic levels of storytelling.
First, we have Merlin - who has been Arthur's servant now for about seven years, declaring that he won't be missed from court because Arthur will be busy with the arrival of The Sarrum and his retinue. Come on, really? That's exactly the time when Arthur will need his personal servant the most - as the episode goes on to show. Merlin isn't stupid. While it's understandable that he is swayed by Daegal's tale, it's totally ridiculous for Merlin to say his absence won't be noted at such a crucial moment in court life.
Then, we have The Sarrum and his men - all deadly killers in a very Saracen-influenced style (from their helms and headgear to their scimitars). We are told again and again what a strong and dangerous ruler The Sarrum is - and we discover that it was he who held Morgana and her young dragon prisoner for two years.
Yet when the assassination attempt on Arthur is interrupted and [SPOILER ALERT] The Sarrum takes the crossbow bolt in the chest instead what do his troops do? Absolutely nothing. They just stand around. Is it ever mentioned again? No. We are led to believe they just shrug their shoulders and shuffle off home, king-less, with nary a bad word to say about Arthur and the splendid hospitality of Camelot!
The central sub-plot of Gwen being in league with Morgana still isn't working for me and this episode did nothing to change my opinion of this serious misstep in the show's direction. It's all still far too reminiscent of Morgana's time in the castle when she was secretly working with her half-sister, Morgause, against Uther.
What a shame that now we know the show is ending in just five weeks' time it hits this rough patch.