The Unexpected Guest is another play by Agatha Christie that was adapted as a novel Charles Osborne - so in short, it is not that great.
Of course I am peeved that I ended up with this book because it was advertised as an Agatha Christie novel, and it is not, but I am also astounded Osborne got to write several novelisations at all, and all of them on commission by Christie's estate!
He has no feel for Christie's characters.
While I can see that the setting in this novel is a typical Christie country house mystery, the main character of Laura Warwick does not strike me as a Christie woman at all.
But maybe I'm just peeved that Audible did not make it clear that this was an Osbone novel.