Alright, I'll try to unpack this without giving away the farm, but seriously, massive spoiler warnings from here on out. The central twist in 'An Impossible Impostor' hinges on the identity of the man claiming to be Harry Haslemere, who supposedly died years ago.
The genius of it is how Raybourn sets up this perfect return-from-the-dead scenario, with Veronica and Stoker initially convinced by his knowledge and mannerisms. You're led down this path of, 'Wow, fate is wild, here's this lost love back from the grave.'
Then the rug gets pulled out. It's not Harry. It's his cousin, Charles. He's been impersonating Harry to claim the inheritance, having studied him obsessively for years. The real twist for me wasn't just the reveal, but the chilling reason Charles gives—it wasn't just greed, it was a lifelong resentment and a warped sense of wanting to become the person he envied. That psychological layer made the whole con way more disturbing than a simple fraud.