Leonard Vole is an unemployed inventor, his latest contraption being a new-fangled egg beater. He is married but through a chance encounter, became friendly with a rich widow, Emily French. When Vole is accused of her murder, his solicitor refers the case to a brilliant barrister, Sir Wilfrid Robarts to lead the defense. Robarts believes his client to be innocent but his alibi rests on the testimony of Vole's wife, Christine. As the jury would expect a wife to defend her husband, he decides not to call her as a witness. He is surprised however when she is called as a witness for the prosecution. As luck would have it, he comes into possession of letters that seriously discredits her testimony. There is, however, a far more devious plot being hatched, one that even the great Robarts cannot fathom.