The life of Bruno Hat is the stuff of fantasy. The reclusive German artist was reportedly discovered by Bryan Guinness, heir to the brewing dynasty, in 1929. The story goes that he pushed open the wrong door in a shop in a Sussex village and found the artist’s avant-garde paintings. He was blown away by the originality and learned that they were painted by the shop-owner’s stepson. Guinness brought the wunderkind to his home in Westminster where he held an exhibition of 20 paintings for the art critics and glitterati. Bruno Hat quickly became the talk of London. It was...