The unexpected guest [adaptation]

In the middle of the night in rural Scotland, Michael Starkwedder has run his car into a ditch and must go to the nearest house to seek help. But downstairs in this house, he discovers a murdered man in a wheelchair and a woman holding a recently fired gun. What seems obvious isn't, and the story that unfolds is classic Christie - a tangled web of lies and cover-ups, where nothing can be taken at face value, and the murderer, and motive, is the greatest mystery of all.