The Secret of the Whistler

The Secret of the Whistler is a 1946 American mystery film noir based on the radio drama The Whistler. Directed by George Sherman, the production features Richard Dix, Leslie Brooks an Michael Duane. It is the sixth of Columbia Pictures eight Whistler films produced in the 1940s, all but the last starring Dix.

He falls in love with Kay. But, Ediths health improves. Then, Edith overhears Ralph professing his love for Kay. Edith threatens Ralph, saying shes going to take him out of her will. So, he decides to poison her, with her own medicine, before she can meet with her lawyers.After Edith dies, Ralph marries Kay. But, Kay becomes suspicious of how Edith died and, worried for her own fate. Finding incriminating diary pages and the medicine, she has the medicine analyzed, discovering that it was poisoned. ........

Source: Wikipedia