Part 2 of a good tale BUT

Question

Why is the imperfect, "tenía que" used instead of maybe the subjunctive "tenga que" or the conditional "tendría que"? In the story it's an action she hasn't yet done, no?

Silvia Piriz · Accepted Answer

Hola Garry M.
In this context ("Diana sabía que tenía que seguir esas pistas misteriosas"), the imperfect "tenía que" is correctly used because it conveys a past intention or obligation that was ongoing in the narrative moment. Although the action (following the clues) hasn't been completed yet, her realization of the obligation occurred clearly in the past—it's something she knew or felt at that moment.
Using the subjunctive "tenga que" wouldn't fit here, as that would typically require a present-time or future uncertainty, which isn't the case. The conditional "tendría que" could express a hypothetical obligation or something she would have to do under certain conditions, but again, it doesn't reflect Diana's clear and ongoing realization in the story.
In narrative Spanish, this kind of imperfect usage is very common to express ongoing thoughts, feelings, or obligations clearly situated in the past.
Hope this helps clarify things!
Saludos
Silvia