One spring morning, a bus full of children and their teachers from a Cotswolds primary school head off on a much-anticipated day trip.But as night falls and the well-heeled parents - one or two of them famous, as well as wealthy - wait at the school to collect their weary offspring, it soon becomes clear that something has gone very wrong.The children and their teachers simply do not come back.What's happened doesn't seem possible.How can an entire class of children simply vanish?