Following the discovery of Lizzie Lancaster's true identity, the women face a race against time to prove Alice's innocence and save her from the hangman's noose. However, subsequent investigations lead to the discovery of a much darker military conspiracy.

Spirited Millie is earning a bit of money selling odds and ends on the black market. But Millie stumbles across a seam of post-Second World War unwholesomeness when she annoys some very dangerous people and gets into trouble. Soon, the other Bletchley girls must rally to her aid.

Lack of action by the police leaves the women to conclude there must be corruption within the vice squad and that catching the gang red-handed is their only option. Plotting to infiltrate the crime ring to find out the location of the hotel being used as a base, they visit Marta in her restaurant, pretending Jean is a potential new client. This leads to an opportunity for Lucy to memorise the businesswoman's ledger, which may hold the key to the whole operation.