1939. When war is declared, twins Shirley and Tom are evacuated to the coastal town of Worthing. Almost fourteen, they are very close to their mother, but leaving London is the only way to keep them safe. Shirley is the bright one of the pair, whereas Tom is sometimes slow to understand the world around him. But Shirley helps him get by and is his best friend and ally.

The twins are taken in by a local farmer, but their new home quickly proves to be far from a rural dream. Tom is forced to do back-breaking work and sleep under the stairs each night. The farmer's wife is heavily pregnant, and seems to live in fear of him. She's refusing all midwives, so it will be up to Shirley, with no experience in the matter, to help her deliver her baby.

Their new teacher at the local school notices that something is not right with the children, but the farmer keeps the twins from seeing anyone, even their own mother. As the cold weather sets in and Tom falls ill, will Shirley be able to find a way out for them both?