The PumpHouse: The Unexpected Guest by Agatha Christie

Through the thick fog of the English countryside, a lost traveler whose car has broken down stumbles up to a manor house looking for assistance only to find the owner of the house, Richard Warwick, shot dead in his wheelchair and his wife standing nearby holding a gun.

But when the police arrive and begin their investigation, they discover that no alibis are foolproof and that no members of the family are free from the entanglements that Richard Warwick tied them up in.