British group Complicité are on tour with A Pacifist's Guide to the War on Cancer, a curious but ultimately moving piece that probes behaviours and attitudes around the disease. It's a little disconcerting at first to have the writer become a character in her own play or for people to play each other but it rapidly becomes clear that the stories being told are actual experiences. And that the show, sometimes at least, is a musical.

It's all rather low-key at first, with the writer Bryony Kimmings atop one of two wheeled towers, grappling with the amount of research and opinion there is about cancer. Later she will recount what happened to her baby son Frank and what happened to Lara Veitch but initially she is simply investigating so she can write a play about cancer for Complicité.

A Pacifist's Guide examines the fears and choices of those who have cancer and the perceptions of those who have not. What do you say to someone with cancer? Why is so much of the narrative about the bravery of those on the front line? This play digs into fears and folk beliefs about its causes and treatment and the terrors of falling into the hands of modern medicine. Lara pushes against the system and refuses reconstructive surgery after a double mastectomy. Young women "need" this to remain "sexually attractive". The play wonders what is said to older women.

There's much more than talk and song. There's a powerful use of imagery. The moment when tiny Frank is put, unseen, through an MRI scan pounds Bryony and the audience with a huge pressure of sound, followed by the barely heard opinions of the medicos. It's a stunning theatrical and emotional effect. And towards the end a forest takes over upstage, as people are lost and found.

Bryony and Lara emerge as central characters, particularly moving in their final scenes, but there's multiple roles taken by all. Eva Alexander is at times a luminous presence, face upturned to the lights, Elexi Walker takes an indomitable stance, usually centre stage, Lottie Vallis has a gently engaging humour and Gemma Storr stands tall with a guitar.

The cast of six move the set, sing and become each other's voices and the voices of the experts, the commentators and the thinkers. If one of them is Susan Sontag or Virginia Woolf their T-shirt will say so. The style is rough but the impact is there, making clear the contradictions in the title's image of a "pacifist's war".

Gentle audience involvement at the end makes clear the ways in which cancer has an impact upon many. And that includes the cast.

Do not be put off by the thought of the subject matter. This is theatre to compel thought about dying and living.