Episode 12.
I had already watched this one on YouTube, and thoroughly enjoyed it.
An Oxford University professor has a relationship with one of his students and he knows that his religious wife would never agree to a divorce, and that's why he decides to kill her.
The professor is played by American guest star Patrick O'Neal.
To me, he usually looks like the British guest star when he's in American TV productions and movies, and there's something about Disney villain Judge Frollo that reminds me of Patrick O'Neal.
Incidentally, this episode aired the day before
The Brothers Series 3 premiere.
If I were shameless enough I would totally copycat James from London's idea and versus these British classics week-by-week. Just kidding.
In this story, the professor has been secretly plotting and developing a Perfect Alibi device, something to do with pre-recordings and a pre-arranged phone call.
I adore this kind of naff technology. Even out of context there's the suspense that something could go wrong. As the viewer I want the evil professor to succeed otherwise there's no story.
But the mechanical dial process doesn't make sense to me as it's being dialed
from a fixed position
to the numbers, instead of, well, vice versa!
After the murder and the visit to his neighbour/colleague/best friend where the Perfect Alibi takes place, he returns home to clear things up and call the police.
There was something surprisingly sad, surprisingly funny
and surprisingly eerie about the image of his dead wife still lying there, eventhough she's been dead for no more than 15 minutes.

And then he starts to receive threatening letters saying "I Know What You've Done!", but without a hint of extortion, which makes sense at the end of the episode.
He suspects and kills two of his students, including the girl he's in love with, but the letters keep coming.
A delightfully misplaced clue "confirms" that it was indeed his best friend/colleague who had sent all those many poison-pen letters.
But in the final twist we learn that the police officer who's investigating the murders has received exactly the same letters - from the professor himself!
A subconscious need to confess, as it were, and the very last moment neatly ties in with the religious vs. agnostic aspect that was only briefly mentioned at the beginning of the episode.
At long last I can rate an excellent Thriller episode.
9/10