 Mark Dightam and his class go on a school trip to the Tower of London. While he is there he loses his pet mouse and vows to return and find her later. Back in school, he is not very attentive and falls asleep during a lesson about electricity so his teacher sends him home. On the  tube  there is a sudden flash & Mark, the train & everyone on it have turned yellow. With the help of Nick (short for  Electronic ) Mark learns about electricity, invades the Tower of London and saves his pet mouse ... or was it a dream. This is the Powell & Pressburger touch applied to children s films.