The Unexpected Guest in Dumb Witness

Jenny: I was really surprised by the depiction of Jan in Dumb Witness vis-a-vis Bella Tanios. It made me reflect on the fact that in Agatha Christie's over in the full-length novels, while we have so many depictions of disabled characters, it's unusual for her to go to the place of mental illness being the cause for murder,. i.e. the murderer being mentally ill. We could conflate or compare to Jan in the unexpected guest. If you would agree with that, and what your thoughts are on that.