The lives of two half-sisters and their drawing master get caught up in a deadly conspiracy revolving around a mentally ill woman dressed all in white.
The dog is shot (offscreen) in episode two, shown briefly injured and whimpering as he is carried into the house, and is revealed to have died (in conversation) in episode three.
No character is confirmed to be autistic (it's unclear whether the "mad" characters are ND, traumatized, or just weird), but if abuse due to/taking advantage of neurodivergence will be upsetting, best to give this story a miss.