India, 1905. Muslim rebels are gathering in the hills, preparing to storm the Maharaja's palace and kill his son, a six-year-old Hindu prince who will be the future leader of the country. The Maharaja appeals to the British to take his son to safety in Delhi. Captain Scott just has time to remove the boy and his American governess, Catherine Wyatt, from the palace before it is attacked and the Maharaja killed.

On arrival at the garrison town of Haserabad, Scott discovers that the last train has already gone, full of Hindu refugees who have fled the city in fear of a rebel attack. However, he locates an Indian engineer, Gupta, who has an old shunting engine which he calls 'Victoria' that is still operational and can be pressed into service. While staying behind in Haserabad and waiting for military reinforcements, the British governor sanctions Scott's escape plan. As well as the prince, Mrs Wyatt, Gupta, and his two Indian subordinates, Scott is accompanied on the journey by the governor's wife, Lady Windham and the governor's secretary, Bridie; an arms dealer, Peters; and a journalist of Dutch-Indonesian origin, Van Leyden, who threatens to reveal their escape plan if he is not allowed to join them and report their story. With the advantage of surprise, they manage to escape, the train bursting through the city gate, which has been guarded by the rebels.

As they proceed, they come across the refugee train, which has been ambushed by the rebels. All the passengers seem to have been killed. Against Scott's advice, Mrs Wyatt insists on searching the train for sign of any survivors, and she discovers a baby, who she brings back and who they name 'India'. Further progress is halted by a broken rail but, by replacing it with some of the track behind the train, they are able to proceed. However, while the track is being repaired there is an enemy attack, and Gupta is wounded before they can make their escape.

At a stop to re-fill the engine with water, Scott becomes suspicious when he discovers Van Leyden encouraging the prince to play dangerously near to the flywheel in the pump-station. Peters has also noticed Van Leyden's reluctance to handle Lady Windham's pig-skin bag and his refusal of any alcohol, and deduces that Van Leyden is a Muslim and in sympathy with the rebels. Van Leyden concedes this but contrasts his values with those of Peters, who is prepared without compunction to sell arms to either side.

Another crisis occurs at a bridge crossing where part of the rail has been damaged. The passengers have to disembark and make their way by foot across part of the track which stretches perilously over a ravine. Scott and the prince almost fall when Van Leyden seems hesitant in passing the boy over to Scott. To the dismay of some of the other passengers, who believe he is over-reacting, Scott accuses Van Leyden of deliberately trying to cause the death of the prince, and places him under armed guard in a separate carriage.

While the prince is on top of the train with Scott and learning how to handle the engine, Van Leyden overpowers the guard and holds the other passengers at gunpoint while he waits for the prince to return to the carriage so that he can kill him. However, as the prince enters the carriage, Bridie manages to kick the gun away. A fight develops on the carriage roof between Van Leyden and Scott and, at the moment when Van Leyden is preparing to kill Scott, he is shot by Mrs Wyatt. The train manages to outpace the pursuing rebel horsemen and arrives safely in Kalapur. Lady Windham learns that a relief army has arrived at Haserabad and that her husband is safe, and Peters resumes his sale of arms. The prince thanks Scott for saving his life but reflects that, in the future, he might be compelled to fight the British to make them leave his country. Scott and Mrs Wyatt are left to find a home for baby 'India'.