Morgana promises to hand over Arthur - who, if you'll remember, killed Odin's son in battle - to the tyrant if he helps her seize the throne. With her father King Rodor (James Fox) still held captive, Mithian rides to Camelot where she's rescued by the kingdom's gallant knights.
Arthur's swiftly taken in by his one-time fiancée's sob story and it's easy to see why - her US show Made in Jersey might've just got the chop, but Janet Montgomery's star is on the rise Stateside for a reason. The glamorous 26-year-old is a talented performer, and it's great that Merlin was able to get her back.
Unfortunately, Mithian's accompanied on her trip to Camelot by the elderly 'Hilda', who's so obviously Morgana in old lady make-up that it makes a mockery of much of the episode, bringing back unfortunate memories of when The Master used to pop up in '80s Doctor Who in some dodgy disguise. Credit where credit's due though; Morgana's true identity is quickly revealed to the viewer - we're not expected to be fooled for long - and her first transformation, glimpsed only as a dark reflection, is a nicely-handled moment.
Only the canny Merlin (Colin Morgan) twigs that Mithian might have been coerced. You'd think by now people would have learned to listen to the young warlock, but instead even Gaius refuses to listen to him, which stretches credibility a little given how much they've been through together.
With our hero's suspicions remaining unproven, Arthur and his knights ride out to rescue King Rodor, though not before we witness an interesting crinkle in his practically perfect marriage with Gwen, as she questions his motives for pursuing Odin. More scenes like this please.
As we reach the episode's midpoint, the pace begins to quicken a little - Merlin learns the truth of Morgana's deception and is very nearly throttled Darth Vader style, and with his friend incapacitated in a kind of magical coma, Arthur presses on unaware and Gaius (Richard Wilson) must use his own magic to save his ward.
But while things pick up considerably from this point, 'Another's Sorrow' is badly lacking in action, falling into the trap of having Arthur and his men walk a little, set up camp, press on further and so on for much of its runtime. We get the briefest of skirmishes 30 minutes in and some decent action at the climax - Arthur's final bout with Odin is suitably tense and epic - but it's too little, too late.
Last week's 'The Death Song of Uther Pendragon' was also relatively light on action, but provided the viewer with some meaty emotional scenes as a substitute. 'Another's Sorrow' offers up nothing so substantial - the complete absence of Morded only increases the feeling that this is something of a filler episode.
That said, it's a filler episode buoyed by solid performances from guest stars Montgomery and Fox - the uncle of Merlin's Morgause, Emilia Fox - and the series regulars never fail to impress. Not the strongest episode of Merlin then, and the weakest instalment of series five thus far, but as a piece of Saturday night entertainment, 'Another's Sorrow' passes 43 minutes pleasantly enough.