THIS is why theatre exists. Islands in the Stream is imagination distilled. It is a wonderfully, sublimely weird work about the sea and water and the things on it and in it. The bald, pale, lean, androgynous cast of two men and two women dance the parts of swaggering sailors, badminton playing passengers, new lovers, playing children and tormented hunchbacks to a score that is sometimes beautiful, sometimes purely terrifying. With sparse staging, expressive lighting and superlative performances, the audience are left on the edge of their seats, open-mouthed. The practically naked performers have a dressing up box of skirts, hats and sackcloth hunchback costumes that they slip in and out of with almost filmic speed.

Sometimes the action is on top of a ship’s deck, with subtly hilarious clowning. But sometimes, somewhere deeper, there is painful, confusing torment. The humour is wonderful, understated and bizarre, with two-dimensional luminescent fish, ships on sticks and cartoon-like characters weaving their way through the dream-like atmosphere. It’s an intense, sensual experience, which prompts both smiles and goosebumps.

Derevo means “tree” in Russian. They are from St Petersburg, and are something of a movement rather than a simple theatre company. Islands in the Stream has its own identity card on the press release, with a date of birth and “special peculiarities”: it “avoids sunlight” and “wears big boots”. Such self-conscious surrealism could be pretentious, but there is such obvious love and belief in this work that in a funny way it rings true. As a rather mysterious voiceover says at the end, the players - they avoid the word actors - are “admirable and lovable”, and the pleasure they take from the performance is palpable and infectious.

Essentially, it is charming, ingenious and indescribable. You have to see it.