Ep 5. Episode Four

From PBS - The women realize there's corruption in the vice squad and decide to intercept the crime ring themselves, with Jean posing as a potential client. Lucy manages to memorize Marta's ledger, but it's written in machine code. Returning to Bletchley Park, they locate an old Enigma machine, break the code and tip off Customs and Excise. But Marta is on to them.