Filmdirector Georges Gachot, a passionate musical documentary filmmaker, became fascinated by the machines used in a factory that produces stamped metal boxes. The machines, with their sonority, rhythms, tunes and automated movements, become musicians and dancers in a show that drive the film to play its cinematic score. The soundtrack, composed with workshops sounds only, unfolds as a musical masterpiece performed by machines for iron and bolt dancers, all coming together in a majestic mechanic choreography. The man who conceived and created these « iron monsters » occupies a fragile place in this powerful, metallic world, which is at the same time incredibly beautiful and musical.