The decoding of Linear B is one of the world's greatest stories. But this story is missing a crucial piece. Two men have dominated Linear B in popular history: Arthur Evans and Michael Ventris. But there was a third figure: Alice Kober, without whose painstaking work, recorded on pieces of paper clipped from hymn-sheets and magazines and stored in cigarette boxes in her Brooklyn loft, Linear B might still remain a mystery. Drawing on Kober's own papers, Margalit Fox provides the final piece of the enigma.

Just before Christmas 1908, Marion Gilchrist, a wealthy 82-year-old spinster, was found bludgeoned to death in her Glasgow home. A valuable diamond brooch was missing, and police soon fastened on a suspect - Oscar Slater, a Jewish immigrant who was rumoured to have a disreputable character. Slater had an alibi, but was nonetheless convicted and sentenced to death, later commuted to life imprisonment in the notorious Peterhead Prison. Seventeen years later, a convict called William Gordon was released from Peterhead. Concealed in a false tooth was a message, addressed to the only man...