Follow four ordinary women with the extraordinary ability to break codes – a skill honed during World War II when they worked undercover at Bletchley Park, site of the United Kingdom’s main decryption establishment. Now, in 1952, Susan, Millie, Lucy and Jean have returned to civilian life, keeping their intelligence work secret from all, including family and friends. A series of ghastly murders targeting women, however, re-unites the team as they set out to decode the pattern behind the crimes.

Part 3 of 3
Following the death of a former spy who had been helpful in identifying the perpetrator, the women consider whether to continue their pursuit. Cleverly planting false clues, the murderer leads Susan into a trap.