In A Breath of Snow and Ashes, much of the settlement come down with dysentery but Claire and Tom Christie, a newcomer, will display different symptoms.
The pair will be struck down with the mystery illness but realising her symptoms aren’t the same as her patients, Claire will decide to investigate.
In the novel it is later revealed Tom’s daughter, Malva, has used the bones of Ephraim, a deceased settler, to cultivate a bacteria.
She uses this to poison Claire and Tom as she hopes to persuade Jamie Fraser (Sam Heughan) he is the father of her unborn child.
source: express.co.uk