This mystery thriller is outrageous and irresistible, an old-fashioned drama with dashes of Patricia Highsmith, Patrick Hamilton, John le Carré and maybe Elizabeth Jane Howard’s memoir Slipstream. It features delicious performances by Helen Mirren and Ian McKellen – I don’t think McKellen has had such a juicy role since his turn in the 1998 drama Apt Pupil – and the film has such storytelling...