Inside Number 9, TV review: Not in the slightest bit funny, but that's no complaint

Inside Number 9 (BBC2) looked at life behind closed doors. After last week's silent-movie hijinks, it was back into the darker recesses of its creators' psyches.

It's always trepidatious when Reece Shearsmith dons the clothes of an ordinary man – something wicked this way comes.

Here we started with Tom, a clean-cut primary school teacher, and his girlfriend (Gemma Arterton). Tom rapidly descended into an almighty funk with the help of a homeless man called Migg (Steve Pemberton).

What began as a study into the unspoken horror of Tom letting the filthy Migg into his house, took a turn for the darker as Migg slowly imbibed Tom's spirit. Or did he? The timing of the "twist" that he didn't actually exist suggested early on that there might be more to come and there was.

This third episode wasn't really in the slightest bit funny, but that's no complaint – I found myself moved by its sad brilliance. Its ambiguity about Tom's state of mind a fine – if cartoonish – take on mental illness. It also featured the glorious line: "You're not Charles Bukowski, you're just a primary school teacher who had a nervous breakdown." So that's one laugh, at least.