Agatha Christie - The Unexpected Guest

After having a car accident, a stranger walks toward an elegant older home, in hopes of being able to summon help. Crossing the lawn, he sees that the house is in total darkness. He approaches a set of French windows and peers inside. Unable to discern any movement, he knocks on the window. Getting no response, he tries the handle and finds it open. Cautiously walking inside, he says "Hello? Is anyone here?" Seeing a middle-aged man sitting in a chair, the stranger says "Oh, I'm sorry. It's this confounded fog. I've just run my car off the road into a ditch. I haven't the faintest idea where I am. I must have run off the main road somewhere. I've been driving around for an hour or more. Are you asleep?" He walks closer to the middle aged man and says "Good God. He's dead". A woman standing nearby says "Yes". Startled, the stranger says "You know?" The woman says "Yes". He says "This man has been shot, through the head. Who?" After pausing for a few seconds, the stranger says "You shot him?" The woman says "Yes. The telephone is on the desk". The stranger says "Telephone?" The woman says "If you want to ring up the police". He says "Well, a few minutes one way or the other won't make any difference. They'll have a bit of a job getting here in this fog, anyway. I'd like to know a little more. Who is he?" She says "My husband. His name is ... was Richard Warrick. I'm Laura Warrick. Hadn't you better ring the police?" He says "All in good time. Nothing wrong with having a cozy little chat first, is it?" She asks "Who are you? How did you happen to come here tonight?" He says "My name is Michael Starkweather. I'm an engineer. My mother's family came from this part of the world. I thought I might buy a little house. For the last two hours, I've been hopelessly lost driving around all the twisted lanes in South Wales. Ended up in a ditch. Thick fog everywhere. I found your gate and groped my way to this house. Tried the handle of the window. It wasn't locked. So I walked in. Whereupon, I find...." She says "the door opens and the unexpected guest comes in".