The killer is in fact Malva's brother, Allan Christie (Alexander Vlahos). He is also the father of her baby, having raped and abused Malva since she was a child. Malva had decided to tell the truth, which is why Allan killed her.
Later, after Claire has returned to the Ridge, she is confessor to Allan Christie, who explains that he was the one that fathered Malva's child, and then murdered her.
Jamie denies having slept with her, but the damage to his and to Claire's reputation is done—and the bond between the Frasers and Malva is severed, until just a few weeks later, when Claire finds Malva murdered in the garden.
Claire eventually realizes that Malva is lying because she knows her husband well enough. Tom seems to question Malva's story.
After sexually abusing her for years, Malva becomes pregnant with Allan's child and he convinces her to claim Jamie as the father in order to save himself.
“He's about 25,” Gabaldon said. It's an interesting response. If you're up to date on the series, then you know that Jamie is not dead at the age of 25.
Malva, before her death, tells him that she made them sick. She'd collected parts of the dead Sin Eater and poisoned Claire and Tom. She wanted to get to Jamie, and getting Claire out of the way was the only way to do that.
Tom Christie admits to having feelings for Claire and knows she's innocent, so he confesses to killing his daughter in order to spare Claire's life.
Malva was first introduced at the beginning of the season as a new resident of the Ridge who admired Claire's medical skills. Behind her admiration was a darker side of blackmail, betraying Claire's trust, and stalking. She falsely claimed Jamie was the father of her unborn child.
Fans are convinced Outlander heroine Claire will be poisoned by Malva after she was seen slicing off a finger of the dead Sin Eater (David Gant) who was introduced in episode two.
Director Brendan Maher told Vulture that while both Menzies and Heughan had stunt doubles for the physically demanding sequence, neither used them much. “We had people for safety, just in case, but the nature of the work is that you want the actors to do as much as they possibly can,” Maher said.
Jamie: "Claire, it was you. It's always been you, and it always will be. Get into bed and put the candle out.
Tom and Claire unexpectedly meet each other with the preacher questioning whether Jamie Fraser (Sam Heughan) was aware of his feelings. In the book, Claire confirms Jamie is well aware of Tom's unrequited feelings towards her and understands them as someone who is in love with her.
Allan began molesting his half-sister Malva from the time she was a young child and eventually, gets her pregnant. She starts sleeping with various men in order to deceive everyone as to the child's paternity.
Malva Christie might have only been introduced in Outlander Season 6, but she has a central role in the drama. The daughter of Tom Christie, she is both naive and sinister, and many Outlander fans have struggled to work out her true intentions.
When Malva was ready to tell Claire the full truth, Allan had to stop her. He killed her to do that, and now he's pushed the blame onto Claire. In the end, Young Ian kills Allan.
Claire is arrested for murder, but Tom learns the truth in the end. It was Allan who did it. It turns out Allan sexually abused and raped Malva, and he is the father of the child. He made Malva sleep with other men and eventually claim Jamie is the father.
She goes on to share all times that they were together, and the first was that night that Claire remembers when she was suffering from the fever. One thing Malva does note is that it wasn't rape and she would never claim that. Claire is so angry at hearing everything that she slaps Malva across the face.
She didn't seem to be doing it for “fun.” Malva just seemed curious, but why would she be curious about that? She's never seemed curious about the intimacies of a couple before. This suggests that she's up to something. Watching the two gives her information to use in the future.
Claire asks Lord John if he believes she (and Brianna and Roger) are from the future, to which he says that he doesn't, but that he will behave for all appearances as though he does.
Instead, he is trying to keep Claire safe as best as he can. There is another reason for this: he loves her. It doesn't really matter about the reasons, though. Tom Christie knows that Claire is innocent, and he should take a huge step in Outlander Season 7 to protect her.
In the "Frequently Asked Questions" section of her website, Gabaldon explains that Master Raymond is not only a time traveler and a shaman, but also a distant relative of both Claire and Geillis.
One night, Claire and John sleep together; afterwards, they both acknowledge: they only had sex as a way to be closer to Jamie. But Jamie isn't dead, and he eventually shows up to find his best friend and the love of his life are married.
Without any relatives to pay the family's debt for the voyage, the ship's captain sold the twins, to be indentured for thirty years against the debt. A man named Aaron Beardsley bought their indenture and brought them to his homestead as servants.
Jamie doesn't really help matters by choosing this moment to confess that he has cheated – but not with Malva. Instead, he spent one night with someone else before going to prison, long ago (and when separated from Claire by 200 years).