We followed the researchers of the joint CNRS / Ministry of Culture scientific project, who have been hard at work since the disaster on 15 April, 2019. Their mission: to unravel the secrets of the 12th- and 13th-century builders as an aid in restoring the edifice. CNRS News presents their initial findings, with a particular emphasis on stone, iron and acoustics, as well as the digital modelling of the monument, a virtual restitution integrating all past, present and future data on the cathedral in an interactive 3D visualisation tool.