You're thinking about tomatoes - Michael Rosen

A sequel to the very popular You're Thinking About Doughnuts. Frank is back among the ruins of the past again, this time on a school trip to a stately home. When the black servant in an eighteenth century picture starts talking to Frank, he really isn't surprised. The girl was Sheba but is sure that isn't her real name and calls herself "Not-Sheba". Frank agrees to help her find out who she is, helped on the way by a celebrity mad mummy, who is desperate to be a star and various statues from India and some exploited Victorian workers. Another witty, zany story that leads the reader through an unorthodox view of British history and the colonial past.