Aging British con artist Roy Courtnay (Ian McKellen) has a new mark — Betty McLeish (Helen Mirren).
He’s developed a knack of researching and locating wealthy widows on-line and setting out to steal their fortunes.
He works with his business partner Vincent, who poses as Roy’s accountant.
After a few dates, Roy fakes a bad knee. He lives in the loft of many story building with many steps, so Betty suggests he stay in a spare room at her house while he recovers.
Betty's grandson Steven is leery of Roy and keeps a close watch on the career con artist.
He discovers Betty is apparently suffering from a series of minor strokes that may kill her within a year, so he knows he must move quickly.
She insists they take a European holiday trip. Although Roy is reluctant to visit Berlin, Betty charms him into accepting a trip schedule that starts there. When Steven meets them in Berlin, Roy knows something is up and the audience becomes aware something happened to him when he was a young British Army officer.
The Good Liar takes it’s time reconnecting the present with 1943 Germany, and what happened all those many years ago.
Soon we find it’s Roy who may have met his match and learn that whatever you do, can come back on you.