The plot of The Nun, which was released back in 2018, was rather straightforward, if you're being kind, or undercooked, if you're being more critical. It boils down to a priest and a nun investigating a haunted abbey with a delivery-boy, with the backstories of the trio only lightly touched upon. By contrast, The Nun II is positively stuffed with plot and subplots, though that's not necessarily a bad thing if you can do it right.
