Absentia tells the story of Tricia's husband Daniel, who has been missing for seven years. Her younger sister Callie moves in with her as the pressure grows to declare him 'dead in absentia'.
As Tricia tries to move on with her life, Callie becomes intrigued by a mysterious tunnel near the house. She starts to connect it to other disappearances, suggesting that Daniel's presumed death may not be 'natural'.
The ancient force lurking in the tunnel seems to have targeted Callie and Tricia, with Daniel possibly facing a fate worse than death in its clutches.