One of the most original pieces of TV writing so far this century came to a close on Saturday night, keeping us guessing right to the last and with a final horrific double twist that left us gaping at the telly in stunned silence. After dispatching Syme’s “best” mercenary last week with scarcely a glance, tonight Hyde took us on a journey to the seventh basement where he finally found redemption.

We had an early clue that Hyde’s end would prove to be a “Harry Potter” moment. Tom, examining his hand, revealed that Hyde had sustained a gash across his palm that Tom didn’t share.

“He’s not passing the damage on,” he mused, “I don’t know why – it’s never happened before.”

It seems churlish, in the middle of a story about a man who changes from a mild-mannered scientist of average strength to a semi-crazed bloodthirsty psychopath with the strength of ten men, to say that this aspect of the story was far-fetched. If he can grow a couple of inches and lose several pounds in the transition to Hyde, change his hairline and his eye colour, then why couldn’t he lose his “damage?” No reason, but it telegraphed the end of the story a bit too clearly for me and indeed when Hyde was being shot up in the cellar, when it finally became clear that he was NOT going to be able to survive the onslaught, then the phrase “not passing on the damage” came clanging back in my mind. Surely not? Surely death is simply too much damage not to “pass on.” Apparently not.

The chambers of Tom clones separated by heavy duty plastic sheets were redolent of Alien Resurrection and sure enough the clones were in various states of Ripleyesque distress. One of them even did a passable impression of a zombie at one point. That could have been even more frightening than it was – a mindless creature with the physical power of Hyde? With even fewer inhibitions on his destructive capability? But no, he just shuffled down the corridor a bit, looking lost.

So was it happy ever after for Tom? Well, he survived. His wife survived. She even stayed sane after watching him change to Hyde, but that’s OK – Hyde died. And his kids survived. It got a bit scary for them in those caskets, but it was OK, because they “swapped.” Ooo-er. A menacing wink from one of them confirms the Jekyll genes are safe and well and living in twin boys somewhere in the south of England. And in mummy too, it seems.

Consistently dark and scary, the six parts of this series have not been a total success for me, but they’ve certainly brightened up an otherwise lacklustre Saturday night schedule, made me jump out of my seat a few times and in the end turned out to be both a grimly satisfying yarn and a very original take on an old horror stalwart. It’s easy to see why Stephen Moffat is one of the most successful (and recognisable) writers for Doctor Who and it’s good to see him being given the chance to branch out. It’ll be very interesting to see what he comes up with next.