In April 1958, three thousand people queued on a Paris street, flanked by the Republican Guard and sipping blue cocktails, to enter an avant-garde gallery that contained nothing at all. The architect of that empty room was Yves Klein, the French artist who claimed he signed the sky as a teenager, composed a symphony of a single sustained chord, and sold certificates for empty space in exchange for pure gold. This episode digs past what looks like an art-world stunt to uncover the philosophical pursuit of the infinite that drove all of it.

We trace Klein from his upbringing in Nice as the son of two painters, through his years as a judo master and student of Rosicrucian philosophy, to the chemical breakthrough that produced International Klein Blue. Along the way we explore the Blue Epoch exhibition in Milan, the Void at the Iris Clert Galle ...