In Arkham Horror, does a third separate instruction after a pair of pass/fail clauses imply that it occurs in both cases?
I think the rest of this cards text is relevant:


  Pass a Luck (-1) check or the book is a prison. If you fail, roll a
  die. On a failure, a monster appears from the book. On a success, you
  are drawn into the book for a time. Stay here next turn.


So, you basically only deal with the consequences if you fail the luck check (due to the book being a prison). The consequences of failing are either bad or worse.

If you pass the first roll, good for you! If not, roll and then if you fail again, you have to face a monster, otherwise, you just get delayed for one turn.

I don't think you can extract some hard and fast rule regarding the sentence structures without looking at them in context.