Too Good to Be True is a 1988 American made-for-television drama film starring Loni Anderson, Patrick Duffy, Daniel Baldwin, Glynnis O'Connor, Larry Drake, Neil Patrick Harris, James Sikking, and Julie Harris.
It was adapted for the small screen by Timothy Bradshaw, based on the novel Leave Her to Heaven by Ben Ames Williams and was directed by Christian I. Nyby II.
When they arrive, a beautiful woman, Ellen Berent, catches Richard's eye and it is revealed that she is also staying at Glen's with her mother, Margaret, and sister, Ruth.
At their lake house, she causes a rift between Richard and the long time caretaker by insinuating that he hit on her.
Richard, inside working, hears Danny's screams for help and rushes out onto the water in a speed boat.
At Ellen's birthday party, she asks Richard to talk to her privately in another room, and she alludes to knowing what is going on between him and Ruth.
Ellen ends up dying, and although initially classified as a suicide, Ruth is arrested and put on trial for murder.
Margaret finds the swapped out sweetener packet and powder residue in the pocket of the jacket Ellen wore at the party.