Although it starts off promisingly, the identity of the killer is a let down as your first guess and their motive turns out to be correct and rather straightforward.
SPOILERS FOLLOW: I'm writing down who the killer is because I sometimes want to go back and check the solution but I can never find this information on the internet and I don't feel like rewatching the whole episode.
At the start of the story you're on the side of Hillary, the daughter who was given up for adoption. I kept hoping she wouldn't be the killer and that she'd end up with the estate after the deaths of her horrid half-sister, mother and grandmother. But in the end it turns out she killed Fliss and Elspeth because she found out she was the child of Elspeth's childhood friend Bishop Richard Deverell. Elspeth and her mother, Naomi, had used this fact to blackmail Richard's father, Augustus, to give them the funds to buy back their manor house. Elspeth and Naomi didn't want Hillary there because they loved her but because she was insurance and she imagined them and Fliss laughing behind her back. Augustus was desperate for Richard to become a cardinal, which wouldn't happen if the fact that he had an illegitimate child got out.
The only real twist, which is quite a good one, is that the disappearance of Cynthia, the wife of Gerald Bennet, who bought the manor house from the Inkpens and later sold it back because it became too much work, had nothing to do with the Inkpens' murders. Cynthia was sleeping around so her daughter, Jane, killed her because she didn't want her father, Gerald, to find out. Jane buried Cynthia in the memorial garden Gerald was creating so when the Inkpens decide to dig up the garden to build a tea shop Jane isn't opposed because it would ruin her father's garden but because she feared Cynthia's body would be found. So when it was dug up she killed her father to spare him from learning the truth.
So there were two killers whose crimes had no connection except proximity. It all ends as a bit of a downer as everyone is either dead or in prison
SPOILERS FOLLOW: I'm writing down who the killer is because I sometimes want to go back and check the solution but I can never find this information on the internet and I don't feel like rewatching the whole episode.
At the start of the story you're on the side of Hillary, the daughter who was given up for adoption. I kept hoping she wouldn't be the killer and that she'd end up with the estate after the deaths of her horrid half-sister, mother and grandmother. But in the end it turns out she killed Fliss and Elspeth because she found out she was the child of Elspeth's childhood friend Bishop Richard Deverell. Elspeth and her mother, Naomi, had used this fact to blackmail Richard's father, Augustus, to give them the funds to buy back their manor house. Elspeth and Naomi didn't want Hillary there because they loved her but because she was insurance and she imagined them and Fliss laughing behind her back. Augustus was desperate for Richard to become a cardinal, which wouldn't happen if the fact that he had an illegitimate child got out.
The only real twist, which is quite a good one, is that the disappearance of Cynthia, the wife of Gerald Bennet, who bought the manor house from the Inkpens and later sold it back because it became too much work, had nothing to do with the Inkpens' murders. Cynthia was sleeping around so her daughter, Jane, killed her because she didn't want her father, Gerald, to find out. Jane buried Cynthia in the memorial garden Gerald was creating so when the Inkpens decide to dig up the garden to build a tea shop Jane isn't opposed because it would ruin her father's garden but because she feared Cynthia's body would be found. So when it was dug up she killed her father to spare him from learning the truth.
So there were two killers whose crimes had no connection except proximity. It all ends as a bit of a downer as everyone is either dead or in prison