A good whodunnit is tightly plotted and gratifies curiosity about the killer and their motive at the end. Huge Davies' Whodunnit is not a good whodunnit.

To be fair to him, he gave up on reading Ronald Knox's Ten Rules for Detective Fiction at the point they became racially dubious, so he's not restricted by the classic rules of murder-mystery fiction.

Arguably the real villain here is the Fringe's £100 early bird discount, which tempts performers into choosing high-concept premises for their show before they've written a word.

If Davies is to be believed, and it's murky, the ton he's saved has been one of his most wretched bargains ever, saddling him with an unwieldy concept, one that he's bolted a disparate set of routines to, wrapped up in a bloody tale of thwarted ambition.

It is, in general, difficult to know what's going on behind his coldly seething, otherwise impassive face and trademark bulky keyboard rig, as he plays mind games with the audience from the first.

Slipping seamlessly, diegetically into his opening routine without formal introduction, affords him licence to belligerently snipe at latecomers. He shares the creepily uncanny tale of a heckler receiving his comeuppance, before deconstructing the gag, establishing its bathos as a pattern he'll be repeating throughout the hour. Touting himself as a charisma-free comedian sets the bar so low that he can only subvert those expectations.

Mind you, him not being Phil Wang appears to have caught one particular journalist off guard, in an amusing tale of racially blinkered confusion that has the tang of authenticity, even if Davies then eagerly takes this case of mistaken identity and runs with it, implicating Wang in other crimes.

At this point, correspondence with reality grows ever more tenuous, as the comic recalls the parents of his recently deceased friend asking him to play Howard Blake's soundtrack to The Snowman at the funeral.

Harping on the differences between the scrappy but ultimately upbeat message of every US Christmas film and the macabre bleakness of Raymond Briggs' British equivalent, Davies' infuriated acquiescence sees him sulkily, sarkily add the famous tune to the jingoistic American triumphalism of Zero Dark Thirty, filling in the hunt for Osama bin Laden with explosive sound effects from his keyboard.

He then much more satisfyingly applies his own lyrics and foregrounds the latent death and bloodspill of traditional British Yuletide festivities. As an isolated four-minute bit, the latter rendition at least, is a winner. And it's followed by a damning characterisation of different BBC radio stations' reporting of serious crimes like murder, with Davies particularly sneery in his dismissal of Radio 1's inanity, his withering, scornful take a delightfully over-the-top sledgehammer to crack a nut.

But thereafter, he takes us into the tortuously over-written and winding account of how he and his surviving schoolmates tried to reconnect after their friend went missing and was presumed dead.

Delivered with almost bored detachment, with the comic only identifying the others by their profession, while ruminating on growing apart with age and different life experiences, this again occupies an odd hinterland between credible autobiography and outlandish fiction, as the body count creeps up.

In the midst of this downbeat, gloomy recollection, there's a tremendous, deliriously unhinged song in which Davies reassures his partner that absolutely nothing happened on his friend's stag do, no insane crime of passion certainly, before we're back approaching the tale's confusing denouement.

There are some uproariously funny set-pieces in Whodunnit. But some real longueurs too and Davies' deadpan doesn't sustain momentum between the music, almost invariably the most successful sequences.