Book 5 in the Christie and Agatha's Detective Agency series! 'Einstein will be all ready to deliver his oh-so-important speech ... only to find that he doesn't have the equipment to deliver it with!' Christie dreams of a train adventure – the kind she's read about in fiction. But Christie and Agatha's journey aboard the Green Express, with company including Albert Einstein, is more than even they bargained for. The twins uncover a plot to sabotage the physicist's radio broadcast, and it's all up to them to thwart it before their journey ends.