The doll in Catriona's grave.
How did it get there? It may have been explained, but I certainly did not get it.
Magnus' sister had that doll, she died many years ago. And her doll ended up next to Catriona's body?
Magnus kept his sister's room like a shrine. Her dolls were there too. On the day Catriona disappeared she had just seen her father with the disgusting mrs. Henry (and no kids seem to have liked her (double shock)). She took the doll from the room/shrine and fled Magnus' house.
Magnus shouted at her - 'I should not have done that' - she ran away to the peat pit 'and that's a dangerous place for kids'
And then: Strange eufemism to that hole in the peat bog a 'grave'ðŸ˜