Two kinds of tension
All writing depends on conflict (without which there is no story), but there’s more than one kind. The obvious kind is steadily building tension with unknown outcome. The battle between good and evil in most stories is like this, though admittedly the good guys usually win.
More subtle is “dramatic irony” where the reader knows what’s going on while the characters don’t. A really effective writer weaves these together for maximum effect, for example Stephen King’s _The Stand_. -m