Agatha Christie help please

[clairethewitch70]

Can anyone identify this book.
The murderer was a young girl. She had a relative (possibly an aunt) who had a terminal illness.

The aunt took the girl out for a drive in her car and drove off an edge, possibly a cliff, committing murder/suicide. Thanks

Crooked House.

Glenn Close played the aunt in a recent film.

Yes, Crooked House. I re-read it a few weeks ago, it’s definitely one of her darker ones!

Thank you. I have the full collection of books just couldn't remember which one it was.