That Dangerous Age

That Dangerous Age is a 1949 British romance film directed by Gregory Ratoff and starring Myrna Loy, Roger Livesey and Peggy Cummins. It was adapted from the play "Autumn" by Margaret Kennedy and Ilya Surguchev. The film was released under the alternative title of If This Be Sin in the United States. It was shot at Shepperton Studios and on location in London and Capri. The film's sets were designed by the art director Andrej Andrejew.
Plot.
Sir Brian Brooke, a famous attorney, collapses while acting as defense counsel in a high-profile murder trial. Doctor Thorvald informs his (second) wife Cathy that Brian needs to rest for six months or he will die; Brian is also temporarily blind. They and Brian's daughter Monica relax in Italy.
They receive an anonymous letter accusing Cathy of carrying on an affair with Brian's junior partner, Michael Barcleigh. Brian's lawyer instincts makes him believe it, until Cathy reveals that Michael has confided to her that he is in love with Monica. Brian is apologetic, and delighted by the news. However, Cathy has lied, and the letter is correct.