'The Perfect Couple' ending explained: Which wedding guest was a killer?

Warning: This post contains spoilers for “The Perfect Couple.”

The culprit behind the death of a maid of honor the evening before a glitzy wedding on Cape Cod remains uncertain until the last episode of "The Perfect Couple."

The six-episode Netflix series, based on the Elin Hilderbrand novel of the same name, begins with the rehearsal dinner for Amelia Sacks (Eve Hewson) and Benji Winbury (Billy Howles).

All appears to be swell on the island of Nantucket, but when the body of the maid of honor, Merritt Monaco (Meghann Fahy), washes up on the shore of the Winbury mansion at the end of the first episode, paradise quickly turns into chaos.

The next episodes show how the Winbury family, and those close to it, begin to unravel before and after the planned wedding date. The last episode reveals the results of the police investigation into who killed Merritt.

Ishaan Khatter, who plays Shooter Dival in the series, tells TODAY.com about his reaction to finding out the ending.

"I, for one, can say it was a very satisfying end, because I genuinely didn't see it coming," Khatter says. "And that's all you want, as an audience for murder mystery — you want to be surprised in a good way. I think it's the first of its kind, in a sense."

Hewson tells TODAY.com that she got an advanced warning about the killer.

"I was told, I think, by Jack Raynor, who had gotten all six episodes, and I had only been given three. I think he like sweet talked (director) Susanne Bier into, like, giving him all the episodes," Hewson says. "And so I was like, 'But who did it?' And then he told me."

Fahy reveals she couldn’t remember how she found out, through laughter: "I must have read it, in the script."

Keep reading for the full ending of "The Perfect Couple," explained.

Who killed Merritt Monaco?

None of the couples in "The Perfect Couple" are anywhere near perfect.

Amelia kisses Shooter after her canceled wedding.

Abby Winbury's husband Thomas Winbury is cheating on her with a family friend, Isabel Nallet.

And Greer Garrison Winbury's husband is cheating on her with Merritt — who had recently told him she was pregnant.

The youngest Winbury son, Will, overheads the conversation between Merritt and his father, Tag, but both are eventually cleared of any involvement in her death due to their alibis.

Police begin investigating Greer (Nicole Kidman), Benjii's mom, believing she had hired a hit man to kill Merritt after finding out she was pregnant. A questionable loan from Shooter backs up the investigators' theory, plus many missed calls from the alleged hit man, Broderick Graham.

Police learn Broderick is really just Greer's brother who needed to pay off a gambling debt. She also comes clean to her family that she was a former escort, Broderick was her manager and that she met Tag while on the job.

Amelia briefly questions Benji's involvement when she finds a slew of photos of Merritt in his drawer, but he tells her that Merritt, an aspiring influencer, had asked him to paint a photo of her to help her Instagram following.

Which leads the detectives to Abby and Thomas.

During Thomas' interview with investigators, he reveals he took some of his grandfather's weapons down to the beach where Merritt was sitting by the water on the night of the rehearsal dinner, but "changed his mind."

However, it was really Isabel who stopped him from pulling the trigger. Thomas tells investigators he owes Isabel about $2 million in debt, which he planned to repay from his trust fund, which he would have access to when Will, the youngest Winbury, turned 18 in a few months.

However, Merritt's pregnancy would have delayed his access by another 18 years, leading Isabel to have a motive for the murder.

Police quickly finds that Isabel had an alibi — she was seen on video footage hooking up with Thomas in the back of a taxi around the time of the murder.

Which leads them to Abby, who had said she was sleeping next to Thomas that night — and who would have a similar motive as Isabel.

The detectives recall an interview with the Winbury’s housekeeper Gosia, who told them Abby had asked her to wash her clothing, bedding and a cup the morning that Merritt’s body was found.

In a flashback explaining what happened, a very pregnant Abby takes pills from her husband's nightstand, and crushes them up to mix into a glass of orange juice for Merritt.

The issue is that Thomas had stolen one of Amelia's mother's pills — a barbiturate that she planned to take if her cancer became unbearable — for a game of "prescription roulette."

Merritt drinks the orange juice, and Abby asks her to go out for a swim, where she holds Merritt underwater, until she dies. The authorities come to arrest Abby at the Winbury home, and she's taken into custody (though she shouts she does not understand her Miranda rights).

After Abby's arrest, Tag smokes a blunt with Gosia, Will reconnects with the police chief's daughter, Isabel yells at Thomas for telling the police she was the culprit and Greer looks out at the ocean, alone.

In the series' final scene, Amelia is now working at the London Zoo, seemingly not with Benji nor Shooter, and Greer comes by to make a special delivery — a copy of her newest book.

Greer asks Amelia to review the manuscript, because it's about her. The pair leave seemingly on good terms, leading viewers to question if are they the true perfect couple, after all?

This article was originally published on TODAY.com