On An Average Day, Comedy Theatre, London

Nostalgic bout of verbal diarrhoea packs little punch

As coffee-loving FBI agent Dale Cooper in the series Twin Peaks, Kyle MacLachlan sought out and eventually confronted his nemesis, Bob – as close an incarnation of evil as has appeared on the television screen.

In this new two-hander by John Kolvenbach, MacLachlan has crossed the country to seek out his nemesis again in the form of Bob.

Except this Bob is his brother, he has not seen him for 23 years and he is a charming, harmless weirdo with serious obsessive compulsive tendencies. Played by Woody Harrelson, he's the sort of guy you pay a fiver to trim your hedge or clear the snow off your path.

Except when the latest good citizen offered him "$20 to clean his bathroom", Bob pushed him out of his car. Unfortunately the car was doing about 50 mph at the time and the good citizen's neck was broken and Bob is facing prison.

This is one of those American plays where there's a whole lot of talk about the past but little moves forward in the present. There are revelations aplenty, a fantastic running gag about a fridge, yet the scanty here-and-now plot is, curiously for such a modernistic play, exceptionally melodramatic and maybe even a touch far-fetched. I don't want to give away the plot, but the sandwich bag with which MacLachlan first enters contains no ham on rye and any dramatist of a previous generation would have simply hung it on the wall and been done with it.

But this is, again like so many of these American plays, an actors' play. And these two certainly act their socks off. Harrelson's performance as Bob is magnificent, rambling and ranting, talking nonsense and making it sound credible, jiggling and trouser pulling, avoiding cliché but implicitly conceding that weirdos can be a little predictable. His tirade about the jurymen at his trial – "freaks and morons and postal clerks" – is little more than we have all wanted to say about those who have opposed us.

Of course, none of this verbal diarrhoea fools his brother. But MacLachlan is still left playing Wise to his Morecambe, stuck with asking the "Do people know what you're saying?" questions at the end of each of Harrelson's flights of mania.

But, in John Crowley's production, there isn't a single non-naturalistic moment. Ultimately the easy naturalism of the dialogue militates against the drama packing a genuinely powerful punch.

At the end, we are left with a wholly believable, quietly tragic outcome and yet it is somehow undemanding, unsurprising and unmemorable.