A Victorian insane asylum. A beautiful but deranged killer. A good doctor who believes in the cure for all ills. And a lot of confectionary. Venus of Broadmoor, one of four plays in Steve Hennessy's Lullabies of Broadmoor quartet, could have been a glorious melodrama, or at least an enjoyable romp. Unfortunately a weak script and little sense of rhythm and tone leave it just the wrong side of mediocre – an opportunity sadly missed in a concept that, on just about every level, brims with potential.The inviting plot introduces us to Christina, sectioned for a bizarre killing in which she left bags of poisoned chocolates for her victims to find and consume. She believes she is the reincarnation of Venus. Our narrator John, another attendant of Broadmoor, seems to think so too and becomes besotted with her beauty and somewhat supernatural charm. She is, as a well-linked set of imagery spun through the script reminds us, both his chocolate and his poison. But the show cannot live up to this enjoyable set of conceits. It only occasionally stops to enjoy its own campness and instead wants to slow things down and present an earnest exploration of its time and trials, rarely letting itself harness the fun or the energy that could spring from its concept.A show like this could have done with some pace, or music, or some more inventive lighting and sound to create something truly atmospheric. It needs a better script, with less laborious dialogue and characters more vividly depicted than the ones here. Take for example Broadmoor's superintendent, Doctor Orange – his dialogue is full of all sorts of detail about the insane asylums of the period, at one point giving their potted history, straight to us, like a man reading from an encyclopedia. It's waxwork acting, with the most perfunctory of characterisations and is reminiscent of the life-size talking dioramas in museums, the ones that tell you about smuggling or the industry of a Saxon village. Yet it would be unfair to blame the cast, some of whom do fantastically with the play's stunted dialogue. The best bits come when they are forced to try something a bit more ambitious, such as the depiction of the child murder victim, something that sees them multi-roling superbly, whilst splitting dialogue with narration in one of the few sections of the play one could call directorially inventive. For the most part, however, it is a series of opportunities poorly met or hopelessly lost. Watching is akin to the experience of being a backseat driver slowly dragged down the motorway – each mile there is a turning, a shortcut, an inviting juncture to explore something new. Yet the car trundles on minute after minute, stuck in smog and dense traffic. There are worse shows at the Fringe, but for doing so little with such a strong set of ideas, Venus of Broadmoor really is murder.