The love affair between Alexander and Laetitia is over. The only way out for Alexander is to remember, reconstruct, to obsessively relive the moments spent together. From the bottom of the abyss that has become his life, nothing escapes, not a detail, an expression, a fragment. His memory is like a filmstrip on which the couple is burned, bright sequences of every moment shared, a grid of shadow and light like a rope bridge over a ravine. The direction and speed of their love – their velocity – becomes the subject of a scientific investigation by Alexander. An investigation of the behavior of light. Of Laetitia. Before he slips down a slope of unrelenting depression. Before he loses all contact with reality.