Rob goes to the local common (aka The Dump) & finds a jackdaw chick there. He takes Joe the Jackdaw home, & keeps him as a pet. Well, he couldn't leave him to die, could he? He causes no end of mess in the house, & then he starts flying into other houses in the street & stealing shiny things from them. The ultimatum comes. Joe must go & live somewhere else. A long way away.
But then Joe discovers green glass. Lots of it. & it's Anglo-Saxon! The campaign to save the common is finally going to work, & it's all thanks to the jackdaw!