The Ending Of Agatha Christie's Crooked House Explained

But why did Lady Edith want to cover up Josephine's crimes? Well, to start, she was never above suspicion, so the opportunity to take the fall was there if she wanted it. She was consistently evasive when it came to helping out with the investigation, never talking to Charles about Aristide's murder, only about the family in general. And when asked when she would be available for a proper interview, Edith replied that she was too busy pruning her flowers. Too busy tending to her garden to help out with the investigation of the murder of a loved one? Very fishy.

We then learn that Edith is terminally ill, with not much time left and no more potentially life-saving treatments on the horizon. Her special bond with Josephine is also steadily developed throughout the movie, with both characters speaking highly of each other and openly cherishing their relationship with Charles. So, with her death imminent, Edith attempts to cover up Josephine's crimes by confessing to the girl's murders, ruining her own reputation to save Josephine from a life of institutionalization and imprisonment. But the only way this would work is by killing herself and the girl so that the truth could never come out, so she drives the two of them off a cliff at a nearby quarry. Unfortunately, the quicklime never destroyed Josephine's tell-all notebook, and Edith's death was ultimately in vain.