The Better Sister ending explained: who killed Adam and who else ends up dead?

​​​The Better Sister on Prime Video is an eight-part twisty-turny thriller that promises to keep us on the edge of our seats until the final moments.

The series is based on the novel by bestselling author Alafair Burke and stars Hollywood favourites Jessica Biel and Elizabeth Banks as 'rival' siblings who have their mysterious past brought to light after a shocking murder. But, as the investigation unfolds, will the siblings manage to reconnect or be torn further apart?

Here is everything that happened in episode 8...

The final episode opens with a flashback to the day that Adam was killed, and we see Nicky waiting in her car for him to get home. He eventually arrives back in a taxi after his visit to the bar, and once he is inside, she walks up the drive and rings the doorbell.

He isn't happy to see her standing on the doorstep and immediately gets cross, telling her she can't be there and that he is going to call the cops. But she tells him to call them, and she will tell them all about how he lied about the day Ethan apparently almost drowned, and that he has been hitting her sister.

Nicky tells Adam that she has been in touch with Ethan and that he has told her everything, and Adam loses his temper, grabbing Nicky and hitting her. When she realises that she's in danger, she tries to escape out of the back door, but he catches her and tries to strangle her to death. In an act of self-defense, she grabs a pocket knife and stabs him in the side and neck, before leaving him bleeding out on the floor and running out of the house and back to the car.

The time then flashes back to 12 hours earlier, and Nicky is at Debbie's house, who is Adam's mom, and she is unpacking groceries for her and catching up. It turns out she drops by a couple of times a week to help out, and they have remained good friends.

Nicky gets a call from Ethan, who is upset as he tells her about how Adam has been hurting Chloe and that the most recent time was really bad. Shaken after the call, Nicky knows she has to do something to save her sister and heads to the store to buy a map and drives to the Hamptons to confront Adam.

We then see Nicky coming out of Adam's house (we now know that she has just killed him in self-defence thanks to the earlier flashback) and she drives home, finding a restroom where she cleans up, tends to her wounds that Adam caused and changes her clothes. She then goes back to Debbie's and uses that as her alibi.

As she gets in the car to leave Debbie's house, she gets the call from the East Hampton Police, which is the moment we first met Nicky in episode 1.

The episode then returns to the present day, and Chloe is shocked that her sister came to save her and Ethan after everything she did to her, and tells Nicky that she won't let her go down for this. She asks Nicky for the knife and gun that she has been keeping, and tells her that she has a plan, but she needs to be out of the way the following day while she puts things into place.

Meanwhile, at the police station, Nancy is telling Matt that she plans to go out to Ohio to see Debbie, and he reveals he has been meeting with someone from the FBI and that he is corrupt, but that he could help them out with a few things.

The next morning, Nicky and Ethan head out for their hike while Chloe deals with the knife and gun that Nicky gave her. But before she can put her plan into action, Jake arrives at her door in a panic. He tells her that he is being blackmailed by Olivero because he has dirt on him due to his exposure to the Gentry Group, which, it turns out, is a corrupt organisation that makes its money by building projects quickly and cheaply by using human trafficking. Chloe is sickened by the revelation that Adam was caught up in this, and Jake says he needs the proof that Adam had on the group to give to the FBI, or they are going to kill him. He also admits that Bill is also part of all this, and he needs to find the paper trail Adam had on Gentry, otherwise neither one of them is safe while the company is still operating.

In the car, Chloe calls the FBI complaints department and files a complaint against Olivero, saying he was physically aggressive and sexually inappropriate with her. The person on the other end of the phone says they take complaints like this seriously and thanks her for calling. She then calls Michelle and asks her for help getting Adam's files they need to help Jake, but Michelle doesn't want to get involved and tells her to stay away from Jake.

Out on their hike, Ethan and Nicky are talking and she asks about a woman who was in court. Ethan admits her name is Helen and that they have been texting, revealing she was going to come up on the train to see him today. Ethan admits he isn't sure if he is up for seeing Helen, though, after the revelations of yesterday, but Nicky tells him it is okay to be cross but not at Chloe, as she only ever had his best interests at heart.

As they are walking, they bump into Ken, who is fishing. He is pleased to meet Ethan, and Ethan uses the opportunity to ask Nicky if she wants to stay with Ken and if he can have her car keys so that he can go and meet Helen. This means Nicky now has no way of getting home, but Ken says he can take her.

Back in Manhattan, Chloe is searching for Adam's paperwork on the Gentry Group in the apartment. She eventually finds it hidden in a secret compartment of their safe. There is also a Dictaphone on which Adam has recorded all the conversations with Bill, and she listens to Bill telling Adam to rinse the Gentry Group for as much as he can and to put the money in his private bank account. Chloe realizes that Adam was scared about being involved with the Gentry Group, but also that he was worried about what the FBI would do if he pulled out of their deal, which is why he was carrying a gun the day he died.

Meanwhile, we see Bill on the phone, telling someone that he has sacked Jake and that he will take care of Chloe. When he gets into his office, he finds Matt waiting for him, who wants to ask more questions about the Gentry Group. Bill is rude to Matt and tells him to come back with a subpoena, which Matt says he will.

At Ken's house, Nicky asks him to show her the bedroom and they sleep together. It is clear she really likes him, but tells him that she needs to go back to Cleveland for a bit, but that she doesn't know if she is going to take Ethan or not, because that is up to him. Ken tells her that he will miss her, just as her phone rings, and it is Chloe, who gives her instructions about where she needs to be.

Back in the city, Chloe visits Chuck and Bill and she gives Bill all of the files that she found in their safe that Adam had on the Gentry Group. Bill is shocked and asks why she is doing this, and she explains that whatever Adam was caught up in got him killed, and that she doesn't want that near her family. She hates being scared of what might happen and wondering if she is next. She says she wants to get back to doing what she loves, but first, she has to put her family back together. Chloe offers her allegiance to him from here on out, and tells him that she will be back in the city in a few days and they should get dinner.

Matt gets some documents delivered to him and calls someone to meet him as he rushes out of his parents' restaurant, while Nicky meets Chloe's private investigator, Jerry, who tells her that he has been digging into Nancy's past and it turns out she beat up the wrong guy on a job, the one she was saying still haunted her during her psych examination, and Nicky is shocked to learn it was covered up. She calls Chloe to say that Jerry came through and they need to confront Nancy, but Chloe tells her she is on her way home and will see her later.

Little do they know, Nancy is in Ohio, screening Matt's calls as she arrives at Debbie's house. She questions Debbie about Adam, what he was like growing up and what his father was like. Debbie admits they hadn't spoken in years, and while she is talking, Nancy gets a message from someone at work who tells her that there is a match on Nicky's cigarette DNA, and she replies asking them to check it against the crime scene DNA.

While Debbie is talking, she reveals that Nicky wasn't with her the whole day Adam was murdered, and that she went away for a bit, even though she had left her phone there. Debbie admits that when Nicky came back to get her phone, that is when she said she got the call from the police to say Adam was dead and had been stabbed. Nancy tells her she is putting together a statement that she can sign, but Debbie refuses. Nancy now knows that Nicky killed Adam, because the fact that Adam was stabbed was never released into the public domain and so only the police and the killer would know that detail.

Nicky turns up at Catherine's house and shows her the file on Nancy. Catherine warns her she will piss off a lot of police with this information, but Nicky jokes that that's nothing new. Nicky asks Catherine to use the journalist from the wake and to do it quickly, knowing it would throw a spanner into Nancy's investigation.

Olivero gets a warrant for searching Bill's home office and gives it to Matt. Chuck lets the police in and Bill is fuming. Meanwhile, Nancy calls her boss to tell him about the statement from Debbie and the DNA match from Nicky, and she is pleased with herself, convinced she is about to pin Nicky for Adam's murder. But her boss has some bad news, because the story about her beating up the wrong person is now all over the internet and he takes her off the case with immediate effect and puts her on leave. A clever move by Nicky, because she knew that Nancy was getting close to working out the truth about who really killed Adam.

As Ethan is driving Nicky home, he reveals that he believed he deserved to be in prison, even though he didn't kill his dad, because he got home that night that Adam was murdered and found him on the floor in a pool of blood. Thinking that Chloe had killed him in self-defence, he staged a robbery and smashed the window... but then, as he was leaving, he also heard his dad make a noise, but instead of calling 911, Ethan admits he walked out and left him to die. He also admits that now he knows about Adam's lies, he is glad that he didn't save him and would do it all again to protect Chloe.

Ethan and Nicky get home just as the news is breaking on the TV that Bill has been arrested for Adam's murder and his involvement in the Gentry Group crimes, too. It turns out that when Chloe went to his house to hand over all Adam's documents, she had also sent a copy of them to Matt, which is how he got his warrant to search the house. But Chloe's pledge of allegiance to Bill was all a rouse, as when he wasn't looking, we see in a flashback that she put the murder weapon in his desk drawer, knowing that the police would find it when they searched his home.

As Chloe and Nicky watch the arrest play out on TV, they relaize that their plan to frame Bill for murder and also get justice for the Gentry Group crimes has worked... but Nancy, who is out of a job and drinking in a bar, sits and also watches the news reports, commenting on how they have got the wrong person, knowing Nicky is the guilty one.

At the end of the episode, we see Nicky and Chloe on the beach at night, sitting around a fire. They both talk about how their new life starts from this moment, and it is just the two of them and Ethan. The pair have got away with murder, got rid of toxic Adam from their lives, and can finally move forward as a family of three.

But - we aren't done yet. In the very last moment, we see a flash of Jake, who is dead on the beach, just outside his house. The show never addresses who killed him, but there is a sense that it could have been any number of suspects. Could it have been Chloe or Nicky, desperate to stop him revealing that Bill has been framed? Or was it Olivero, the crooked FBI agent who had been blackmailing Jake? The gentry Group could have had him killed for being an informant for the police, or perhaps the whole thing had got too much for Jake and he took his own life?

One thing is for sure: we need season 2 to get the answers!

All episodes of The Better Sister are available to stream worldwide on Prime Video now.