I've been critical of this series before, but little could prepare me for how abysmally bad the fifth and final story, The Last Breath, was.

The third and fourth parts hadn't been too bad, especially the one of those not written by the show's creator. But any semblance of continuity, or even logic, got thrown out of the nearest hatch pretty early on.

It started well enough, with a nice twist where the meek survey station operator Hatsuto turned out to be an oil company agent, but from there the plot and performances sank to the oceanic depths.

The wholly predictable reappearance of Clem, not dead, only then to kill him off in a scene where everyone does something remarkably stupid, was ridiculous. Clem attacks Stas, one of the people on the Volos that could help him, then Vincent alerts Raymond to Clem's attack allowing him to shoot Clem, and then Captain Zubov operates a weapon that killed most of his crew without any idea in what direction it's currently pointing.

The collective stupidity of this scene was shocking, but it didn't really resolve how Vincent was still alive after being heavily irradiated, or how Clem got out of the mini sub, pressurised for the abyssal trench, without exploding or at least dying of decompression sickness.

I'm not even going to grace the mind numbingly dumb elements that followed this, where the naff design of the Orpheus colluded to nearly kill all of those onboard, because by then, I'd concluded that the writer had no idea how to end this narrative without stitching things together in a totally unnatural and disjointed way.

The worst examples of this revolved around Svetlana. I had to watch her scenes through at least three times before I had any idea of what happened to her, and it still didn't make much sense. She dragged an air bottle (I assume it was air) to the Volos moon pool to find that mini sub Lurch wasn't there any longer, and the next time we see her, she's in the Russian mini sub dying under the ice!

Well, the Russian mini sub wasn't in the moon pool in any of the earlier shots, and what was the point of having her escape to then expire? That meant nobody ever knew what happened on the Volos, or even why it exploded. She might as well have died on the Volos and they could have saved the entire £4.50 they spent on her mini sub effects.

I was also slightly taken aback by the total lack of any concern from supposedly environmentally sensitive people to a huge release of radioactivity under the ice, or that the friendly whales helping them find the ice hole will all be dead very shortly. These and a hundred other details were just too much trouble to address, it appears.

The last twenty minutes were the most painful, where Catherine and Samson get to rejoice about how much smarter they are than the company stooges, while enjoying a romp in bed. In the end, I wanted this show to end so much, it was actually a relief when it finally did.

My assessment of The Deep was that claustrophobic sub dramas can work very well, as long as you keep a grip on the realities of the situation, but this show never even tried. The lack of understanding about depth and pressure was patent from the outset, and the show never stepped away from insulting the intelligence of its viewers when it was decided that something impossible should happen. Yet, an arguably greater crime than that, it didn't even have a very engaging story, and the whole Russian's versus American Corporate oil companies guff was like a rejected plot for Spooks.

Mix that with some dire acting, bizarre casting and substandard (pun fully intended) effects and I can't see anyone demanding a second voyage of the Orpheus.

Given how excellent Sherlock was, this exercise showed that not everyone at BBC Drama is on the same page, it appears.

Read our review of The Deep episode 4: Everything Put Together Falls Apart here.