If you've ever been anywhere near the Fens you'll probably have realised that they're fucking mental, but if unlike me you haven't visited Spalding's Springfields Centre for a fun day out then Jez Butterworth's The Night Heron will serve as an equally adequate introduction. A dark comedy which gets full marks for both darkness and comedy, it opens with two unemployed gardeners in a hovel-like house in the middle of nowhere, and closes with a kidnapped student sprawled naked over a chair. In-between there's fervent religious cults, suspicions of witchcraft, simmering violence and incongruous poetry recitals. This is East Anglia. We get bored.The acting is mostly excellent, a lot more human and naturalistic than I've seen in more classical productions from director Will Maynard Rob Hoare Nairne as Wattmore has the perfect blend of reserved shyness and intense fear, his diction as fussily clean as Jacob Lloyd's as Griffin is rough and angry; though at times, particularly earlier on, I felt Lloyd could have been rougher still around the edges. Kate Lewin is absolutely stunning as Bolla, a scenery-chewing ex-con with occasional glimpses of pathos and deep-seated insecurity, her deep London voice perfectly matched to the character's bullish, Pinteresque disruption of this fragile household unit. A couple of smaller parts, Royce and Fowler, paled in comparison to the virtuosity of these three leads and could have done with a clearer sense of character in their brief periods onstage.The writing is impeccable, hardly surprising given Butterworth's recent smash-hit with Jerusalem themes, images and hilarious knife-twisting flashpoints of dialogue rise suddenly and fall away, like half-glimpsed figures in the ever-present mist.