In the second episode. We see Helena spend a lot of time with her cousin George Batt. He is an amiable old duffer.
George also spends a lot of time with Alex Vesey and his second wife Ruth. Helena is unaware of this.
In fact everyone does well hiding things from Helena. Kit and Angela with their newborn child have been mingling with his father's family who is also due to be knighted.
Ruth Vesey is a renowned photographer. A television documentary on her shows a glimpse of George Batt in their garden. Helena watches this on television and is seething at George.
Helena has always hated Ruth but now sees an opportunity to get rid off her and pin the blame on George.
The documentary gives a clue to a sweet spot where Ruth appears vulnerable. The rest is Helena using her cunning.
Ruth's demise is very well written by Andrew Davies. In contrast with Helena she is a lovely caring woman. Her death is slow and you always hope that there is a chance that she will be saved.