The Northern Song Dynasty painting “Listening to a Zither (Qin)” depicts a private gathering of noblemen, with one man dressed as a Taoist playing the traditional Chinese instrument and an audience of two wearing official attire. The artist was long believed to have been Emperor Huizong, who handwrote its title and asked his grand counsellor, Cai Jing, to inscribe a poem on the work. The question is, who is the mysterious zither player? Professor Li Song from Peking University shares his finding