I've started the first book of the Outlander series, Outlander by Diana Gabaldon.
From the author's website:
In 1946, after WWII, a young Englishwoman named Claire Beauchamp Randall goes to the Scottish Highlands with her husband, Frank. She’s an ex-combat nurse, he’s been in the army as well, they’ve been separated for the last six years, and this is a second honeymoon; they’re getting re-acquainted with each other, thinking of starting a family. But one day Claire goes out walking by herself, and comes across a circle of standing stones–such circles are in fact common all over northern Britain. She walks through a cleft stone in the circle….and disappears. Back into 1743, where the first person she meets is a gentleman in an 18th-century army officer’s uniform. This gentleman, Jack Randall, looks just like her husband Frank–and proves to be Frank’s six-times-great-grandfather. Unfortunately, he also proves to be a sadistic bisexual pervert, and while trying to escape from him, Claire falls into the hands of a gang of Highland Scots, who are also trying to get away from Black Jack Randall–though for other reasons.
In order to avoid being handed over to Captain Randall, Claire is obliged to marry one of the young clansmen. So she finds herself trying to escape from Castle Leoch and her Scottish captors, trying to get back to her husband Frank, trying to avoid being recaptured by Captain Randall–and falling in love with Jamie Fraser, the young man she’s been forced to marry.