When someone sits down to write a musical, it's rare that they dream up a piece of work that is befitting to a small performance space, shying away from spotlights and microphones and a 1500-seater auditorium. Refreshingly, Alexandra Spencer-Jones (writer) and Patrick Gleeson (composer) have done just that, and tell you what, it works.Their musical opens with two girls - Constance and Sinestra - sat centre-stage, a projector overhead setting the scene for the story that is to commence. They've recently lost their mother, now stuffed by their taxidermist father to remain forever in a corner of their home. When neighbours drop by to check on the children, temptation to step outside their house starts to rise, and what follows is a thrilling and sometimes upsetting combination of Tim Burton and Hansel & Gretel, with plenty of music in between.As a musical, Constance & Sinestra is far more than another Tim Burton-like piece, but the company themselves make the comparison to his work. This story is like a Grimm fairy tale, where what could have been charming and uplifting is subverted and suddenly dark. It's still a pleasure to watch, and musical numbers blend marvellously as they vary between teary laments and comedic character pieces.Rather than simply singing, actors also take part in much of the music-making. Some songs are accompanied only by a backing track - a shame - but others involve actors playing a combination of a piano, cello and the double bass over or instead of a backing number. This actor-musician divide is wonderful when actually used, it's just not utilised enough. In particular, Tom Whitelock's Hale could be further established in the play. Whitelock's cameos on the main stage as a door could easily be transferred to the creation of other human props, while his brilliant background movements on the piano and his creation of sound effects with all manner of objects are, I fear, lost in the emotion and drama of the rest of this musical.Constance & Sinestra takes a while to get off the ground but when it does it's great. It's not confusing, but it does introduce ideas that could be developed further, like Hereford and the Mad Dad's rapport. The problem is that a lot of good ideas aren't fully realised. Perhaps this a by-product of time restrictions at the Fringe? This show clearly has a lot of promise, and in later incarnations will surely become even greater as it is stretched and thickened out further. For the time being, Spencer-Jones and Gleeson have provided Action to the Word and the rest of Edinburgh with a beautiful little show, which isn't anywhere near as frightening as it may at first seem.