Warning: This definitely contains some plot spoilers

Hmm. Well, that was a disappointing ending, certainly on a comedic level, to what has undoubtedly been my personal highlight of the BBC's broadcasting calendar thus far in 2009. With a few loose ends left untied, it's possible that there may be a second series or at the very least a spin-off involving some of the characters who didn't bite the dust - presuming those that did leave us last night really have gone for good. Who knows as the series took a few strange turns last night that undid much of the excellent plotting the series has seen so far.

Worst of all was the reappearance of Nurse Kenchington, the key plot device of the whole show. Bringing her back to life was a mistake for me, I'm afraid, and all the stuff about her lost locket - is there any more significance to that trinket? - simply distracted from the real reason the characters had been led towards Ravenhill Hospital in the first place. Turns out that the mystery blackmailer was Mr Jolly all along, having faked his own decapitation in the previous episode, much to the shock of Jelly and his beshackled lady friend. Unhappy at the group's murder of Kenchington during their stay at Ravenhill, he was out for the ultimate revenge, and what better than to blow them all up with a big bomb.

The characters' route to the hospital was laid out last week so this episode was all about reunions and revelations as Joy and Oscar, plus hangers-on Tealeaf, Mrs Wren, Nicola and Oscar's new carer Jennifer were all present to learn about the real reason they were all there.

Oscar had his own personal battle to deal with too as the hunt for Snappy the Crocodile came to something of an abrupt end for said toy, now quite possibly several leagues under the sea. Learning how Oscar's determined search for the toy was inextricably linked to his stay in Ravenhill and his final exchanges with Tealeaf were actually rather moving. Lomax has proven to be a more rounded character than on first appearances and I was sad to see him go.

Joy's own madness took on new heights this week as her precious Freddie made it to the bottom of the bin and Jennifer was mistaken for him, giving Dawn French plenty of space to gag about how her now grown-up baby still needed to mind its language. It was a far cry from the horrors of the blood baby of last week and made for some light relief for a character that was steadily becoming the stuff of many a nightmare.

The episode's primary focus shifted this week back to not-as-into-murders-as-you-first-thought David. After visiting Citizens Advice about his murders - brilliantly satirising the ineptness of such organisations - and not forgetting to take his bag on his way out (turns out it just had a huge watermelon in there all along) he then turned up at Ravenhill and began to hear the creepy tones of Kenchington.

David, firmly convinced of his part in her 'murder', is revealed as actually quite a gentle soul who just happened to lose it while practising for Ravenhill's big musical number for the visiting governors. Understandable, really, given Kenchington's downright torture of the poor lamb. Clearly inspired by One Flew Over The Cuckoo's Nest's Nurse Ratched, only far crueller, it was good, if frightening, to see just how disturbed she truly was. This insight was also necessary to set up the murderous act the troupe carried out, Robert in particular taking great enjoyment out of their own brand of revenge.

It was once more down to Jelly and old Mrs Wren to supply the bulk of the laughs for the episode and they were as strong as ever, if too few for my liking. The scene in the service station toilets was a classic moment, the reaction of a cleaning lady witnessing the sight of a young boy with his hands in his pocket of a clown handcuffed to a collapsed old woman proving pure comedy gold. Just as good were Mrs Wren's comebacks to Jelly's questions ("In the war we went in our neighbours' pots and pans." "Didn't you have a toilet?" "Yes. We just didn't like the neighbours.")

The biggest laugh of all for me, though, was in one of the episode's smaller moments. After arriving at Ravenhill, Jelly calls out to see if anyone is there. "Hello," he says to which Mrs Wren answers, quite sweetly, "Ello." They are a fine comedy double and kudos to the creators for making an old woman such a star.

I've left Robert and Kerry's tale until the end as it seems that they, like David, might be back for more in a future series or spin-off. In a plot right out of a Grimm's fairy story, they ended up completely separate from the others as Robert was privy to Kerry's own disturbed state of mind. With poisoned soup, an old crone of a 'grandmother' and the location of Kenchinton's locket revealed, it was an odd treatment of a couple of characters who came into their own last week. With the locket only just established moments earlier and Kerry's reasoning behind kidnapping Robert, nor the character of the grandmother, being clear, I was left feeling disappointed by how Robert's part in all this ended. And why would he have forgiven Kerry so quickly after their altercation in the previous episode?

In a series that has cranked the comedy and dramatic horror up to 11, I wanted more from this finale and was left feeling a little let down by last night's offering. It wasn't bad by any means and had it not been for the final, confused ten minutes or so, I think this could have been great. Indeed, another five minutes onto the episode to clear things up more would have been welcome. As it stands it was merely quite good and for a series this strong that's ultimately a bit of a misfire.

Still, as whole this has made for superb Thursday night viewing and no matter what the boys go on to do next they can rest assured that they have created a new set of memorable characters and a sense of style to die for. Can it be executed so well a second time round? We may yet find out.

Check out our review of episode 6 here.