Lady of Hay by Barbara Erskine
Ms Erskine is always recommended whenever someone mentions timeslip novels, and this is widely regarded as one of her best. I bought the 25th anniversary edition, which has an extra chapter at the end, covering what happened to the characters in those 25 years and with an extra twist or two. It's a whopper of a book - I bought the paperback but at over 800 pages think it would have been an easier read on my kindle.
It has a huge an complex plot. In the present day (well, mid 1980s) journalist Jo Clifford is experiencing regressions to a past life - that of Matilda, a lady from the 12th century. Jo's got trouble in her private life - the love of her life Nick has left her and is seeing someone else. Nick's brother Sam is a hypnotist, and can make Jo regress back to the 12th century and be Matilda for a while. He has her best interests at heart - or does he?
Matilda is married very young to a brute of a nobleman, and in her complex history has several children, consorts with Prince then King John, has a love affair with another man. She's a real character who actually existed at that time, and you can tell the author has done a lot of research.
I found the whole reincarnation thing a bit far-fetched, especially as Jo/Matilda isn't the only one in the book. Everyone seems to have been someone else from that time. I know you have to suspend disbelief when reading any book that has a supernatural element, but for me, this one pushed me a bit far without having an adequate explanation of why it was all happening and why these people were targeted as hosts by the long-dead historical characters. Having said that, I very much enjoyed this novel. Erskine is a superb story teller, and I loved the historical strand of the story.