In the early hours of 9 July 1994, the deputy director of London's Tate Gallery, Sandy Nairne, is woken with devastating news. Two of the gallery's most valuable paintings have been stolen while on loan to the Schirn gallery in Frankfurt, Germany: JMW Turner's Shade and Darkness, and Light and Colour.

The news sets Sandy off on a six-and-a-half-year mission to recover the paintings, which together are worth over £24 million, that leads the police on a journey to the Belgrade underground.