The idea is Ish is a strange one. A first time author goes to Big Finish towers (probably by email but indulge my image of a huge building, possibly in the shape of a bald head) and pitches the idea of a virus-like word fragment which infects people at a philological convention. You would expect them to be shown the door. We live in an age where most people have a vocabulary of about twenty words, five of which are variations on "fuck". We also live in an age where verbosity and pretentious pronouncements are irrevocably linked with Pip and Jane Baker. One can only imagine what they would think if they ever heard Ish.

"It’s almost as educational as one of ours, Pip" Jane might comment.

"Yes dear" replies Pip.

It begins with some bickering between the Doctor and Peri. Unlike much of season 23 the bickering is both good natured and well written as it focuses on the Doctor’s apparent (assumed or genuine) disgust with the American corruptions of English. One might be tempted to question why he cares as he’s not actually English (or British come to that) and some, all or less of his linguistic talents come from the Tardis’s telepathic circuits.

We are then plunged into a murder mystery – a locked door, an obvious suicide, a curious lack of motive – as the Doctor tries to find out who killed his old friend Osefa. We are also introduced to the strange customs of the information age. Peri has lunch with an apparently charming young wordsmith called Warren and manage to pay for their nosh by listing lots of words beginning with the "peri-" prefix.

The expert at listing words is Book – the artificial intelligence created to catalogue every word in the English language. For once Big Finish get a voice distortion effect right. They are experts are replicating pre-existing voices (Daleks, Cybermen, Ice Warriors et al) but their original efforts usually leave a lot to be desired. Book is a welcome exception. His voice has just enough expression in it to not get boring to listen to while never letting us forget he is only a holographic projection created by a computer.

Add in a splendidly out-of-his-depth convention organiser, Cawdry, a joke borrowed from Blackadder the Third and a script which never once either talks down to or overwhelms the listener, and you’ve got the makings of a very good play.

Unfortunately, it all goes wrong when the Big Bad turns up. Although the idea of a single word being repeated ad nauseum by the brainless masses is a familiar one to anyone who has lived in a region where "muppet" has taken hold as a one-size-fits-all phrase, a sentient word fragment is just too bizarre a concept. A few billion years ago the universe was created. A sonic wave was generated which travelled through space. Eventually this sound found someone to hear it and the omniverbum was born. Or something. Anyway, this sound creature wants to survive and so spreads itself from host to host. A familiar conceit attached to an extremely convoluted premise.

So a very promising story quickly turns into a cross between Whispers of Terror and Dictionary Corner and I really can’t remember what happens next. I’ve fallen asleep during Ish a great many times. All I can remember about the last episode and a half is some kind of contraption which beeps whenever anyone says "…ish". I know there is a lot of bafflegab and a fair bit of moralising but it is an unsatisfactory resolution.

I know they wanted to do something different rather than simply have Book go mad and start killing people but sometimes the obvious route is the best. Ish could’ve become the anti-Hitch Hiker’s Guide (where the lead AI is also called (the) Book) rather than the Invisible Enemy without the comical prawn.

But I still like it more than most of you.