This is a summary based on my understanding of the novel. Please also note that this summary contains spoilers. You may want to read the entire book first before proceeding
Rose & Fern Castle are fraternal twins – they are nothing alike. Rose is short, Fern is tall. Both also differ in personalities.
When they were kids, they grew up under the care of their mother, Nina, who only seemed to care about Fern. Nina also has a bad temper, so Rose made sure to protect Fern.
Now at 27, Rose is married to Owen, while Fern is working in a library. They have dinner at least once a week while Fern visits their mother on Thursdays. Rose doesn’t visit their mother, they never had a good relationship.
On one of their dinners, Fern saw Rose’s vitamins for pregnancy. She admitted that she and Owen have been trying for a baby, but they are finding it difficult. She’s worried she might not be able to bear a child, but she’s constantly looking for ways. Fern didn’t mention it but she thought about giving Rose a baby – she’s healthy, she knows she can bear a child. She’s pretty decided about getting pregnant, she just needs to look for the right man to have sex with.
She met Wally (real name Rocco) – she has mistaken him for a homeless man. She calls him Wally because he wears a hat like the one from Where’s Wally. They got to know each other, went on a date, then had sex. Fern really enjoyed Wally’s company that as they made love, she even forgot all about getting pregnant for Rose.
Rose finally met Wally. Rose was in London for a few weeks to visit Owen. When she got back, she met with Wally inside Fern’s house. She was worried at first since Fern mentioned that he lives in a van, so basically homeless. However, Rose did some digging and found out that Wally is a multimillionaire – he’s a computer programmer who developed a successful app and sold it.
Fern got pregnant, and Rose was the first one she admitted it to. Rose was worried that both Fern and Wally are incapable of raising a child. Fern with her forgetfulness and high sensitivity to light, sound and touch. Wally with her tendency to be unstable – based on the fact that he moved out of the country when he got overwhelmed by his success.
Rose scheduled Fern to a planned parenthood clinic – but changed her mind at the last minute. Rose suggested that Fern can give the baby to her. That was actually Fern’s original plan, and it now makes sense because she wants her baby to have loving parents who are always around – Rose & Owen. It was decided – but first she needs to end things with Wally.
Rose also suggested that she move in with her, she built a little house in her backyard where Fern could stay. Fern agreed and also had some help on how to break it off with Wally – she told him that he found someone else. Wally accepted that, and before he left, he warned Fern about her sister. Fern didn’t listen.
Fern also told her mother that she’s pregnant, and that she’s going to have Rose take care of the baby because she is more capable. Although speech impaired due to drug overdose years ago, Nina managed to warn Fern not to give her baby to Rose. Fern didn’t understand why her mother would make such warning. She mentioned this to Rose – who got bothered.
While she was nearing her due date, Rose went to the library Fern was working on and brought the news about their mother’s death. It shocked Fern, especially when during her weekly visits, her mother seemed to be doing well. She phoned the facility her mother was in and found out that Rose visited, and she was the last person Nina saw before she died. Fern got suspicious.
Fern also met with Wally, he went to the library to talk to her. He was quite stunned to see how pregnant she was. Wally asked her if she was okay since Rose has contacted him, and told him that Fern is in need of cash assistance. Fern denied that, and wondered why Rose would do that. Wally also claimed that Rose has been giving him a visit, inviting him for coffee, after he and Fern broke up.
When Fern was about to give birth, she had no choice but to contact Rose. Rose was a great help during the delivery. Fern later on realised that she doesn’t want to give the baby to Rose – and that she also doesn’t trust her after everything she learned about her. She ran away from the hospital with her baby, whom she named Willow, and headed to the library to call Wally. She wasn’t able to contact him – and when she got out to get a better signal, she was greeted by policemen, with Rose. Willow was later on taken away from her and the next thing she knew, she was already in a pysch ward. A doctor and a detective was there to talk to her – she talked to the detective first.
Fern previosuly thought that the detective was there due to kidnapping charges – becauase she took Willow, which was supposed to be Rose’s. The detective clarified that she was there because of Nina’s autopsy reports – and Rose is the main suspect. They found out that Nina has been injected with insulin from her hairline, and Rose has access to insulin since she is diabetic.
Fern got another visitor – Owen. He clarified that he was not in London at all, he was in another town because he decided he could no longer fix his marriage with Rose. Rose also told him previously about the adoption, which he never agreed to.
Fern got another visitor – it was Wally, and she was finally able to tell him that it was his daughter after all. Contrary to what she thought previously that Wally doesn’t want a child – he turned out to be a willing and great father when Willow was finally handed back to them.
Wally and Fern moved in together and took care of Willow. Fern continued working on the library. Wally sold his second app and earned a lot of money. Meanwhile, nobody has ever visited Rose yet.
Rose is still in jail – and all she has is her journal. She drafted a confession where she wrote the real truth:
She admitted that Fern didn’t kill Billy – even though that was what she made Fern believe. Billy is the son of Nina’s boyfriend. Billy died during their camping. Fern felt guilty since then, because she and Billy was competing on who could stay underwater the longest, and she helped him stay down – as per Rose’s instruction. Rose has been in a foul mood since she started liking Billy, and she just saw him kiss Fern. She told Rose to keep him down while she looks at the time. Fern said 40 seconds – Rose lied about the time since she intended to kill Billy, and blamed Fern. As they were recovering Billy, Nina arrived – she asked the girls what happened. When Fern answered, she already knew that Rose made her do it.
Rose tried to kill Nina 16 years ago. She didn’t have drug overdose, she injected insulin into her hairline with the intent to kill her – but she lived and only had brain damage.
She also admitted that she planned it all out – leaving the pregnancy vitamins for Fern to see. She planned on how Fern would act, she planned on how she could get the baby.
Ofcourse, she wasn’t going to confess that easily. So she tore up that confession she wrote and started a new one – she plans to narrate the events differently, so she could blame Nina’s death on Fern.
The End of The Good Sister by Sally Hepworth.