Assist the Steamwheedle Cartel in stopping the sinister Crown Chemical Co. plot.
You will receive credit for this achievement when you complete the required quest chain and kill http://www.wowdb.com/npcs/36296-apothecary-hummel and his cohorts. You'll need to be at least level 89 in order to use the Dungeon Finder tool to queue for The Crown Chemical Co.
For Horde players, the quest chain starts with http://www.wowdb.com/npcs/37172-detective-snap-snagglebolt in Orgrimmar with the quest Something Stinks. (There is a breadcrumb quest called Uncommon Scents that you may pick up from http://www.wowdb.com/npcs/38295-junior-detective.) To see the full quest chain, click the spoiler.
For Alliance players, the quest chain starts with http://www.wowdb.com/npcs/38066-inspector-snip-snagglebolt in Stormwind with the quest Something Stinks. (There is a breadcrumb quest called Uncommon Scents that you may pick up from http://www.wowdb.com/npcs/38293-junior-inspector.) To see the full quest chain, click the spoiler.
Trivia: Prior to 2010, this achievement was named "Nearest and Dearest" and was awarded by completing the Love is in the Air storyline quest beginning with the Dangerous Love (A)/(H) quest.