According to Diana Gabaldon, six of the upcoming Season 3 episodes are very close to the book.
Did Frank Become Unfaithful?Diana Gabaldon also said that the mystery on whether or not Frank Randall (Tobias Menzies) cheated on Claire (Caitriona Balfe) would finally be settled in the coming season. In the book, Gabaldon left this part ambiguous and let the readers decide whether or not they will hate Frank.
I personally don't think this is so mysterious but maybe that is just me.
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