A Special Book

Unfortunately, ordinary coordinates and TomTom won't work in Karazhan.
But I know navigating Karazhan can be quite daunting, so I resorted to pasting maps with a single marker on them.

If you know the way to the [npc=15691] yourself: Skip to point 14.

1. 
   
2. Entrance of old Karazhan: /way #42 46.89 74.75 Old Karazhan entrance
3. 
   
4. Climb up the stairs behind this mark: https://www.wowhead.com/maps?data=3457.1:519608
5. 
   
6. At the top of the stairs, re-open your map, locate and kill [npc=15687]
7. 
   
8. Climb up the stairs at: https://www.wowhead.com/maps?data=3457.3:713391
9. 
   
10. Enter the backstage area at: https://www.wowhead.com/maps?data=3457.4:260220
11. 
    
12. Speak to [npc=16812] who will spawn a random boss for the "Opera Hall" boss mark on your map
13. 
    
14. Leave the stage at the other Exit you did NOT use enter it
15. 
    
16. Climb the stairs at https://www.wowhead.com/maps?data=3457.5:615199
17. 
    
18. Exit the Opera Hall at https://www.wowhead.com/maps?data=3457.6:425360
19. 
    
20. Climb some stairs and exit the room at: https://www.wowhead.com/maps?data=3457.6:641669
21. 
    
22. Climb some stairs to reach the exit of the map "Lower Broken Stair": https://www.wowhead.com/maps?data=3457.7:534594
23. 
    
24. Climb some more stairs and exit the map "Upper Broken Stair" at https://www.wowhead.com/maps?data=3457.8:539491538491
25. 
    
26. You are now on the map "The Menagerie". Re-open your map, locate and kill [npc=15691]
27. 
    
28. Using your [item=207730], you have to find 4 [object=408976] in a specific order, the last of which is [item=208889]. All 4 tomes are in bookcases; ignore those lying on the floor.
29. 
    
30. First Tome: https://www.wowhead.com/maps?data=3457.9:309479
31. 
    
32. Second Tome: https://www.wowhead.com/maps?data=3457.9:356356
33. 
    
34. Third Tome: https://www.wowhead.com/maps?data=3457.9:463624
35. 
    
36. Fourth Tome / [item=208889]: https://www.wowhead.com/maps?data=3457.9:321498
37. 
    
38. [item=208889] starts the quest [quest=77908]. Go back to [npc=207696] to finish it.
39. 
    

The reward of this is the part "Kirin Tor Knowledge" of the achievement Whodunnit?

Thanks to Xemnuz and foogoo for your additional infos in the comments, I have added them here :)

absolutely bloody brilliant, i hate Karazan and always get lost. thanks for this :)

For those that know the way through the raid, just go to the Curator and continue from number 14 on Tieffliegers list. I started following each step in case I had to do something, but at 14 past Curator is when it starts. Thank you, Tiefflieger, for the post!