It's mystery project day! In an echoey mobile classroom the teacher duplicates a map for her class. It shows their route from the village school into Ipswich including a bus ride and six road crossings. The teacher gets fraught at a couple of near misses in spite of her careful warnings of risk. A disembodied male voice delivers advice from the Green Cross Code - will they all survive the trip? Evocative school atmosphere and scenes of Ipswich and surrounding countryside.