The case that ingenious detective Mr J G Reeder is working on is more than just a case. It is a suitcase. And the suitcase in question is "... a handsome article ... no maker's name was visible on the inside, or owner's initials on its glossy lid." The woman who had carried the case "... must have the strength of a navvy ..."
Mr Reeder has to find out about the contents of the case and discover more about its carrier, 'Mrs Jackson'. The Stealer of Marble is Casefile Number 4 which is also included in Casefile Numbers 1, 2, 3 and 3 from 'The Mind of Mr J G Reeder' by Edgar Wallace.