CGI animation. Ernie, controller of International Underground, is always on hand to help his friends and to get passengers to their destinations. He is helped by trains Victoria, Bakerloo, Circle, Jubilee and the twins Hammersmith and City. Ernie and Millie organise a surprise party for Mr Rails, but Ernie has a bad cold so he leaves Millie in charge of the party plans. Without Ernie's help she has a busy day trying to get everything ready.