The 4 deaths in this episode (one from the past) brings the total in the series to date to 148.
There are parallels with the first episode, "The Killings at Badger's Drift."
Elizabeth Spriggs played Iris Rainbird and Richard Cant played her son Dennis in the first episode, "The Killings at Badger's Drift." They play the Goodings in this episode, sister and cousin to the earlier murder victims. Barnaby notes the resemblance, and Ursula Gooding inherited her sister's snooping nature.
Another parallel with the first episode is that a death of a woman named Bella predates the present day action, Bella Trace by shotgun in the first episode and Bella Slade in "Dead Letters."
The murder victims:
1. Marion Slade- Drugged and drowned
2. Mark Castle- Drugged and throat slit
3. Dr. Wellow- Stabbed to death
N/B- Historical death of Bella Slade; died after an abortion