Skåne, 1986:

On the night of Walpurgis, the eve of May Day, where bonfires are lit to ward off evil spirits and preparations are made to celebrate the renewal of spring, a sixteen-year-old girl is ritualistically murdered in the woods beside a castle. Her stepbrother is convicted of the terrible deed and shortly after, the entire family vanishes without a trace.

Spring, 2019:

Dr Thea Lind moves into the castle. After making a strange discovery in an ancient oak tree on the grounds, her fascination with the old tragedy deepens. As she uncovers more and more similarities between her own troubled past...