Enduring Song: oh dear. Jesse Briton's in-the-round Crusades epic, set alternately in France and Turkey, is a real mess of a show; a prime example of why writers should never direct their own work.

Our main character is Matthew (a strong Tom Roe), set to inherit his father's ailing farm, trapped into a marriage with the hysterical and pregnant Jennifer. He doesn't quite know where to turn, so when Peter, Bishop of Amiens, rocks up with an evangelical proposal to join him on the road to Antioch and later Jerusalem, he finds himself enticed into joining him, along with friends Georges, Hugh and Gaston.

While there's potential in this idea (see the National's production of Ibsen's Emperor and Galilean for a historical, religious epic that stunned and sparkled), the reality here is pretty tedious, and Briton strikes his point a little too hard. Clocking in at just under three hours with a minimal interval, there are some lovely moments in this historical melange (mainly the beautiful, resonant singing that punctuates the piece), but they are few and far between.

Briton has over-indulged himself directorially, writing exacting stage directions that hamper his cast, leaving in numerous flabby scenes and jokes that add nothing to the potentially interesting plot, and worst of all, under-directing numerous members of his cast, clearly overwhelmed by numbers. This results in a great deal of yelling and not much nuance.

This leaves us with a real mix of performance levels. Rafe Beckley provides an excellent central presence as patriarch Robert, while Daniel Foxsmith and Emma Ballantine give outstanding, highly emotive performances as Matthew's friend Georges and sister Marie. Meanwhile, Moncef Mansur and Sibylle Bernardin have great chemistry and provide good comic relief as church guardians Ibn and Sibylle. Unfortunately, as Gaston, Jac Husebo is completely incomprehensible, garbling and shouting all of his lines. Eloise Secker does her best as deserted, pregnant Jennifer - it's clear she's a strong actress, but Briton's unbalanced writing makes it difficult to feel for her later on, when her personality seems to have undergone a thorough overhaul.

Alex Harland, meanwhile, is nigh on unwatchable as Peter, so ‘big' is his performance (yes, he's evangelical, but even then it becomes too much), and for this, the guilt must lie, in the main, with Briton. Harland's speeches are unfortunately reminiscent of the post-death booming dramatics of the appalling Damned By Despair, another example of where, like Southwark Playhouse, a theatre can swiftly swing from sublime to ridiculous. At some point, Briton should have told him to turn it down. At some point, he should have told himself the same thing.