Mary Brown was a pickpocket in London in 1899. She had to give her pickings to her crime boss. She attracted the interest of cab-driver Bobby Stamford, who later witnessed a Justician from Jalxar crash-land in a marsh, Bobby using the reassembled robot and other equipment to set himself up as a vigilante targeting Mary's 'employers', as well as leaving her some money.
When Mary tried to track her anonymous benefactor to the church where Samford kept his equipment, she ran into the Fourth Doctor, Romana I, Professor George Litefoot and Henry Gordon Jago, who had been tracking Stamford's vigilante identity at the same time. Mary's 'boss', Harvey Marsh, also followed Mary, and planned to execute the Doctor, Litefoot and Jago while forcing Romana to work for him with Mary, but this plan was cut short when the Justician was unleashed on Marsh's men. Stamford sacrificed himself to save Mary when the robot detected her guilt over her crimes and nearly shot her.