And Even More Past Perfect Problems

(Grammar Questions I Couldn't Answer)
I've written about Past Perfect problems twice before (HERE and HERE).   But another grammar question has come up. 
This one comes from a grammar worksheet gapfill on the past perfect.  The students have to answer each gap with a form of the word in brackets either in the past simple or the past perfect:

I had been warned about the dangers in Peru, but no one (1/tell)______ me how incredibly beautiful it was.

The teacher scheduled to teach this lesson was asking around for the answer, and none of us could decide. 
Although looking at it now, it looks to me more and more like it should be past perfect.