London, 1920. The three Bentley children are used to fending for themselves. Their widowed mother has been forced to take a night job at Grant's clothing factory, and sees them only at breakfast and on Sundays. But at nearly eighteen, and with a job as a housemaid to help make ends meet, Dora is well able to look after her younger siblings Tom and Lily. Then one morning their mother fails to appear for breakfast, and when Dora is told by the gatekeeper at Grant's factory that no one by the name of Harriet Bentley has ever worked there, the children grow worried. They know their mother loves them, and cannot believe she would deliberately deceive them. With the help of a neighbour, a former policeman who was badly injured during the War, Dora and her siblings start to investigate.