Sally Harrup, an orphan of 17, lives in the Plymouth dockside slums with her sister Ruth. They can barely remember their mother and never knew who their father was. Ruth supports them both by working as a prostitute till she became too ill. Sally gets a job with a local bakery, is befriended by her employers Grace and Alfie Philpott, by fisherman Ethan Shields and his family, and by Captain Eva Cassington, who runs the local Salvation Army refuge and is trying to stamp out the trade in rounding up young girls, sent on Belgian brothel ships for the sex trade in Europe.
Two of the Philpotts' regular customers are closely connected with the ‘trade', and when they learn that Sally has thwarted them in rescuing Rachel, a girl of 11, from them just in time, they are intent on revenge. Sally returns home to find Ruth dead in suspicious circumstances. When tragedy strikes Rachel too, Sally blames herself, and Grace Philpott virtually disowns her. Then Sally discovers her father's identity. After finding papers Ruth would never let her see while she was alive, she goes to confront Robert Sanderson, a butler at nearby Lanhydrock House who tells her she is making it up, and has her arrested on a trumped-up charge of theft.
She is soon released from prison without a stain on her character, but her whole world is gradually collapsing around her. Only the Shields family, Captain Eva, a sympathetic police inspector, and the local chairman of the police authority, stand by her. To show her gratitude, Sally agrees to help take part in Eva's desperate last-ditch attempt to save the girls from the brothel ships.
This synopsis report prepared by John Van der Kiste