Firking was a cobbler. He and his fellow cobbler Hodge encountered Ian Chesterton and Barbara Wright in a tavern. After causing a bar fight to break out which resulted in Barbara being kidnapped, they offered to help Ian in the future should he need it.
Later, when they thought Ian was in danger in the cellars of the Houses of Parliament and went there to rescue him, they discovered Robert Hay there instead. Hay was about to set off a gunpowder explosion, but the cobblers managed to overpower him. (PROSE: The Plotters)