I have been watching the Marlow Murder Club and find it very interesting. I especially enjoy Samantha Bond. I find it quite a coincidence, I also saw her right after this show on a repeat of Mid Somer Murders. She was also in a Morse episode.

Where?

You can watch 3 episodes, but NOT the 4th, on Prime Video.
You can watch all 4 on Apple TV on the PBS channel. However, you will find, as I did, that you will have to join the PBS Passport thingy. That cost me $5 a month; but includes access to a bunch of PBS programs. May as well drop the PBS Masterpiece channel on Prime video.

We enjoyed it; but it's over the top unrealistic.