Rose Armstrong, a semi-retired archivist within MI5, discovers an anomaly in the old files. It becomes obvious that there was a monumental deception in the past, but who was deceiving who? Someone in today's world of intelligence will stop at nothing to prevent her continuing her investigation. The murder of Rose brings her two devoted friends Ann Barron and Jess Maclean, both ex-MI5, out of retirement. Both now middle aged mothers with family responsibilties, they unofficially set out to find Rose's murderer. They also become embroiled with the deception and whoever is determined that the deception should not be uncovered at any cost. They are on their own - or are they? Someone seems to be keeping watch over them and does MI5 really not know what they are doing? In the end, the deception is real but not what they had thought, resulting in the identification of a spy within MI5. Finally, a meeting in Moscow explains why the deception took place and who was deceived.