Roy Courtnay (Ian McKellen) is an aging British con artist who, along with his business partner Vincent (Jim Carter), manipulates people into giving him access to their finances through a string of deception and false identities. In 2009, his latest target is Betty McLeish (Helen Mirren), a former history professor at Oxford who lost her husband a year ago and has savings in excess of £2 million.Feigning a bad knee, Roy manipulates Betty into allowing him to stay at her house. He steadily encourages her to open a joint offshore investment account with him, so that he can steal her money. Simultaneously, Roy and Vincent run an investment scam with their mark Bryn (Mark Lewis Jones) and his associate by employing fake Russian investors (Roy pretends to "invest" 200K pounds and the fame Russian investor puts in 800K pounds, to encourage Bryn to part with his funds to the tune of 400K pounds, with a promise of quick doubling of the money). One of the fake Russians, actually a Polish butcher, demands a greater cut of the take; in response, Roy orders thugs to break the butcher's hand with a meat tenderizer. Realizing he has been robbed, Bryn follows Roy during his date with Betty. Upon spotting Bryn nearby, Roy sends Betty into the shops before luring Bryn into Charing Cross tube station. There, Roy subdues Bryn by stabbing and then shoving him into the path of an incoming train, killing him instantly. Roy flees and reunites with Betty back at the shops.Roy and Betty vacation in Berlin, where Roy appears to understand German, though he claims he does not. Betty's grandson Steven (Russell Tovey) then takes the couple to a flat that Roy recognizes and Steven reveals that 'Roy Courtnay'-a young British Army officer-was killed there in 1948 by a Nazi war criminal whom he was tracking, according to Soviet records. This causes Roy to explain that his real name is Hans Taub (Laurie Davidson), who was Roy's German translator, and that he stole Roy's identity so that he could leave Germany and reinvent himself. Betty accepts his explanation and dismisses Steven's objections.Soon afterwards, Roy and Betty plan to transfer their money into the joint account. Vincent suggests to Roy that he leave at least some of the money for Betty to help with her medical condition, but Roy dismisses the idea and insists that he'll leave Betty financially defrauded just like his previous victims. Vincent reluctantly complies and later observes the couple transferring their money into the joint account. However, after leaving Betty and returning to his flat, Roy discovers that he no longer has the keypad needed to access the account. Roy returns to Betty's house to reclaim it, only to find Betty waiting for him and that all the house's contents have been removed.Betty attempts to force a confession out of Roy, before revealing that her identity and personal history are all fake. Her real name is Lili and she and Roy have met before as German teenagers in 1943, when Hans was tutoring her in English. On their last session, Hans sexually assaulted Lili (Hans wanted to have sex with Lili's older sisters, but they made fun of him and insulted him, so he took his revenge on Lili). After her parents dismissed Hans from continuing his tutoring lessons, he denounced Lili's father as a traitor and he was executed by the Nazis. This drove Lili's mother to commit suicide. Later, Lili's sisters were killed in an explosion just two weeks before the death of Adolf Hitler. After the war ended, Lili made her way to England.After recounting on their past, Lili explains to Roy that she has been fully aware of his plan to con her all along. Steven, who was in fact the boyfriend of Lili's real grandson Michael, tracked Roy/Hans' criminal history and they confirmed his identity in a DNA test using a locket from Betty/Lili's childhood that contained a piece of Hans' hair. She also reveals that Vincent has betrayed Roy after being confronted with her knowledge of their crimes.Betty takes all of Roy's money out of their joint account, leaving him only enough money to pay back the victims of his earlier con. Just as she prepares to leave the house, Roy locks the door and attacks her - but she manages to fend him off before he is confronted by Bryn's associate and the Polish butcher whom he previously cheated. Betty then leaves the house as Roy, refusing to pay his clients back, is consequently beaten up. Weeks later, Roy is shown in hospital - virtually catatonic - while Betty is shown living happily with her extended family.