As an opera writer and reviewer I ask tenor John Longmuir, who plays Maupertuis in the concept film of Émilie & Voltaire, which classic opera role attracts him the most. He names Don Ottavio from Mozart's Don Giovanni and I am surprised, having always seen Ottavio as somewhat ineffectual. I also wonder whether Ottavio was really in love with his wronged fiancée. John coolly considers he 'probably' was, and gives me another vision of him, as strategist. Rather than wasting energy on futile challenges, Ottavio plans revenge on Don Giovanni by gathering aristocratic allies.

I suddenly see links between John's concept of Ottavio and the way he plays Maupertuis. Maupertuis is a man of action, but his tactics are calculating: when he sets out to woo Émilie to Paris he is full of praise for her scientific knowledge, not his own. His conversation is seductive and he implies that he's a more than worthy rival for Voltaire but he never actually says that he loves Émilie. Does he? Even I, having written his lines, cannot quite be sure, even as he delivers them.

Only once, when after a long pause he sings just her name, and pauses again, do I think that probably ...