Johannes and the curator Alexander Eiling are standing in the Städel Museum’ storage room – in front of an empty picture frame. It is the frame that once held the “Portrait of Dr Gachet”, which was in the Städel collection until 1937. The present owner: anonymous. The museum long made every effort to obtain the painting as a loan for its upcoming van Gogh exhibition – in vain. Instead, the empty picture frame will serve in the show as a reminder of the work’s breath-taking history. The tale begins in Auvers-sur-Oise, a small town outside Paris. It is there that van Gogh paints the portrait of his doctor just a few weeks before he commits suicide. How is the painting linked to van Gogh’s own biography? What makes it a masterwork?