Grace begins seeing strange things in the house. A mirror shows scenes from both the past (like the Colonial executions) and the future. She finds what she believes is her mother-in-law engaged with two others in some kind of ritual, and sees blood dripping from her mother-in-law's mouth. Attempts are made to explain these things away; Garce is in a new and unfamiliar environment, her husband is not around much, the stress of having a new baby is affecting her, and she was a former junkie all suggest that she might be just hallucinating.
When Grace's Priest shows up to bapitize the new baby, but instead has a vision of flames and becomes ill, Grace becomes convinced that something is not right with her new life.
While the film gets some credit for its production quality, but the acting and plot leave something to be desired. I have a feeling that the film is trying to achieve an air of mystery, but suffers from giving away the ending (the film is called Witchcraft so you expect there will be something to do with witches and magic), and being too much like Rosemary's Baby (which, by comparison, does not reveal the key component to its plot in its name).
If you are interested in the series, then you want to start with the first film, which lays some of the foundation for the second. Most the rest of the series is made up of films that stand on their own.