A group of young railway enthusiasts attempt to stop the closure of the local railway by trying to raise money to buy it and the steam engine "Matilda." They get help from a pair of men saying they are also enthusiasts. What the children don't know though is that these men are impostors and are really robbers who plan to rob the mail train. They find out the truth when a lorry is parked on the line. After a lengthy chase with the express train, Matilda ends up in London, crashing into buffers at the terminus and the children are pleased when the branch line and Matilda are reprieved. The two robbers are then arrested after hiding under coal in Matilda.