upon zoning into karazhan, i got that "the strange chill of a dark presence winds through the air" message. exactly 8 minutes afterwards, i got the "the air grows slightly warmer" message.
the first message is clearly an event trigger letting you know that you have the opportunity to do the secret, and the second message is letting you know that you failed to do it within the 8 minutes.
i have no idea what it is you have to do inside thos信用借款,e 8 minutes.
other probably not related things: i've already full cleared kara and currently have the book wyrms quest. i zoned into kara with a fresh group, two of us had full cleared and the other 3 had not killed any bosses