The Snake Pit
Undset, Sigrid
Set in medieval Norway, The Snake Pit follows Olav and Ingunn, who, though raised as brother sister, have become lovers in a world caught between the fading sphere of pagan worship and vendettas and the expansion of Christianity.

Olav Audunsson and Ingunn Steinfinnsdatter became lovers with they were barely beyond childhood and endured a long and bitter separation before they could wed. Now they are beginning what each hopes will be a new life -- but in Ingunn's past lies the shame of an illegitimate child and Olav's past lies murder. And the guilt they carry may prove more destructive of their happiness than all the years they spent as outcasts.