Inside No. 9's Curse of the Ninth bends the rules – and hits a bum note

The story takes inspiration from a real-life superstition, which references the deaths of various classical composers during or soon after the writing of their ninth symphony – from Beethoven in 1827 to Tishchenko in 2010.

The story starts with a bang. Literally. Eddie Marsan's composer Nathaniel Burnham shoots himself in the head as a sinister figure emerges from the shadows behind him, leaving his own ninth unfinished.

It's a bold start that immediately hooks your attention, which makes it all the more disappointing that the rest of the episode can't maintain such momentum.

On the contrary, it proceeds to slow down considerably. Where most chapters of Inside No. 9 boast a fizzing comic energy or a creeping sense of dread – and sometimes both – Curse of the Ninth fails to achieve either. The absence of the latter is particularly disappointing, as this premise is ripe for atmospheric sequences that never quite materialise.

One element that gets in the way is what could be interpreted as a slight bending of the titular rule, with the episode lacking a keen sense of being "Inside" No. 9. There's an argument to be made that the '9' in this episode is the symphony itself, rather than the location, or that the mansion of widow Lillian (Natalie Dormer) – and the garden outside – is still one setting. Perhaps.

But the freedom with which the characters move about prevents this episode from developing the intense claustrophobia that pervades Inside No. 9's creepiest instalments. Jonah simply comes and goes as he pleases, including for one outdoor scene in the manor's garden as he digs up Nathaniel's body to pry sheet music from his cold, dead fingers. It sounds scarier than it is.

Indeed, for a story about a curse, this instalment has remarkably few moments that truly get under the skin, with James Swanton's personification of doom used so sparingly as to barely leave an impression. One can't help but wonder if a Hill House-style strategy of subtly placing him in certain shots might have been an effective way of maintaining a sense of peril throughout.

Then again, that might have been a hard trick to pull off, given that most of this episode unfolds in broad daylight. I'm not sure if I've ever seen a story about a supernatural spook that has so many brightly-lit scenes – besides maybe It Follows, which uses its daytime sequences to amplify the terror of its central premise.

In contrast, Curse of the Ninth plays out like a somewhat generic period drama, only with a light sprinkling of awkward humour and a midpoint exhumation. Shearsmith, Pemberton and Dormer are all on fine form, but there's nothing particularly compelling or even interesting about their characters, and consequently, no reason to fear for their safety or hope they achieve their goals.

Instead, we're just waiting for the inevitable sting – and it comes in the closing moments, right on time. Jonah finishes Nathaniel's ninth symphony, but hands the written document to Lillian with one page missing, which had been hidden inside the late composer's piano earlier in the episode.

Passing off his deliberate ploy as an honest mistake, he hands the final sheet to the widow, who happily places it in the book – effectively meaning it is she who has finished her late husband's symphony. On this technicality, Lillian swiftly meets a violent end at the hands of the curse in a twist that leaves us feeling empty.

Sure, the character was far from virtuous, and that makes her fair game by horror story logic, but nor was Jonah, who brutally killed housemaid Devonshire (Hayley Squires) and seemingly gets off scot-free.

Supposedly, he now scoops up the pages around Lillian's broken body and lives out the rest of his days as a celebrated musician – his youthful ambition. Hooray?

Curse of the Ninth has all the promise and ingredients of a spooky period piece, but winds up as the most forgettable entry in Inside No. 9's final season (so far). Here's hoping this is merely the calm before a barnstorming send-off next week.

Inside No. 9 is available to stream on BBC iPlayer.

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