In his 1662 work The History of Imbanking and Draining the Fens and Marshes, and of the Improvements Intended thereby the Royalist antiquary William Dugdale recorded the anonymous ballad The Fowler's or Powte's Complaint. "Behold the great design, which they do now determine, Will make our bodies pine, a prey to crows and vermine : For they do mean all Fens to drain, and waters overmaster, All will be dry, and we must die, 'cause Essex calves want pasture." Usually people complain about being driven off the land but here the Fenmen were complaining about being driven off the water and onto the land, impinging on the traditional way of life and reducing the ability to hide amongst the marshes from the authorities. The shadowy Hereward the Wake would never have been able to slip away from the Normans into the misty Fens.

Four and a half centuries on from Dugdale the fears of the seventeenth century seem to have not been entirely realised if Jez Butterworth's The Night Heron is to be believed. The Fens are still a mysterious and treacherous area where people still go to lie low, where the rule of law is tenuous and where visitors may well be in danger. Watmore and Griffin are lying low even if they are locals, exiled not from their native land but the educational metropolis of Cambridge by dint of unfair dismissal. Wrapped in a blanket and recovering from a beating by person or persons unknown Simon Lee's Watmore is by his own declarations and those of Griffin "a good man". But is he? And is Griffin really his friend? Why then does he reveal his secrets to all and sundry, deride his religious revelations and give away his sleeping accommodation? There is, as is often mentioned, "A storm coming".

The odd couple receive a series of visitors unwelcome or strange, or in some cases, both. Michelle-Louise Wright's Bolla Fogg (or is she Fiona?) has answered their advert in The Bugle for a lodger but how has she come to the area and why? And why does she slyly conceal a knife up the sleeve of her jumper? She was odd, menacing and vulnerable by turns, switching moods as quickly as you blink, alternately towering and cowering. I particularly treasure the memory of her "appearing" on the kitchen table like demon in Fuseli painting. A fine achievement. Fen Ditton is a place where you can tell insulting stories about your childhood acquaintances and still expect them to be standing next to you at the bar. Martin South's impressive Neddy Beagle (another member of the disunited varsity gardening brethren) is an old school frenemy of Griffin's now acting as a go between for blackmailing head gardener and dog killer Floyd Farmer. Dickon Farmar's Royce is on a yet lower rung of the green fingered brotherhood and a (very) special constable - Griffin derides him "It's not even half a copper. He's a volunteer. He does it for free". I enjoyed his performance all judicial authority collapsing into a gibbering mess at first contact with a real criminal. No Ipswich promotion for him. And that is before we have met Bernard Brennan's becloaked pound shop cult leader Dougal, derided by Griffin as the lowest of the horticultural low - "a leafblower". I fully expected him to bring in his own wicker man, although made from local reeds, obviously. Honourable mentions to Richard Pedersen and Eliza Insley as the latecoming Norwegian birdwatchers looking for a glass of clean water in an ocean of insanity and Sam McQueen as the drugged student and possible angel recalling Shelley even in his stupefaction. The principle duo of Watmore and Griffin were superbly realised by Simon Lee and Roger Beaumont the former tone perfect in his fatalism and undermined by his religious mania, the latter tricky and amusing in presenting Griffin to us as a caring jester while possibly being a violent thief. Both very welcome and intelligent returns to the stage.

The play does have some resemblance to Butterworth's later work The Winterling although in the former the locals are threatened by the arrival of outsiders and in The Night Heron any outsiders are threatened by the locals. The danger of being beaten over the head for your binoculars would surely categorise a trip to the area as "extreme birdwatching". What is the meaning behind the marshy iconostasis? There are very strong hints of a Christian message. A small group of believers regarded as weird by everyone else, a re-appearance of a figure seen by very few and a good man seemingly sacrificing himself having taken on the sins of others so that a greater good is served. And that is before we get into an exile from a garden which leads to the moral decline of all concerned.

Debut director Fred Janaway can be justly proud of marshalling a fine company in such an impressive and moving way. The interaction of the characters was particularly notable, never a gesture missed or a look wasted. All opportunities for comic relief taken with aplomb. I particularly treasure the memory of Roger Beaumont's Griffin extinguishing and re-lighting four candles (no, not those ones) in the face of a temperamental power supply. That along with the group literary interrogation of the kidnapped student by flickering road lamp "Who in the field of poetry do you admire and why?" marked out Robin Snowdon's lighting design as particularly fine. Rob Ellis's sound design with storms, bird cries and some very wry local radio announcements "There's a church fete in March. That's March the place not the month. If you turn up in March you'll have missed it" wrapped the whole play in a misty and menacing atmosphere that was clearly never going to lift to reveal sunshine and lollipops. Everyone was suitably costumed by Lily Ann Green for a place where the writ of Gap and H&M surely does not run. And all set on a superb Rosie Shipman/Michael Bettell/Keith Syrett set dingy and decaying as a perfect surrounding for the dingy and decaying scenario.

To return to Powte's Complaint : "The feather'd fowls have wings, to fly to other nations; But we have no such things, to aid our transportations; We must give place (oh grievous case) to horned beasts and cattle, Except that we can all agree to drive them out by battle." The bird may have flown , but the battle will be never ending. I saw three performances and could quite easily have seen the other three as well and never been bored for a second. If you missed it, you missed a treat. Maybe we can hope soon for a trip to The River if not Jerusalem itself.