You will have to face three tough boss fights similar to the three drakota in Fire and Ice along with a treak through Death Fist Citadel. 

Your first order of business will be to head back down to Nagafen's Lair. Nagafen will be very upset, however talking to him you assure him that you are confident enough to take down Darathar. Nagafen will give you a ring from one of the drakota he managed to kill that attacked him. He will then tell you there are four other drakota that you must kill for their rings in order to reach Darathar.  

• Vault of the Fallen: Lair of Trenda'Loz
• Sanctum of Fear: Drakota's Lair
• Firemyst Gulley: Vanudozalon the Elusive
• Death Fist Citadel: Assault Instance

Trenda'loz is probably the easier of the 3 drakota bosses so it's best to start in the Vault of the Fallen.  The same can be said for the Drakota in the Sanctum of Fear.  Vanudozalon is a bit more tricky in that you have to find and kill his illusionary drakotas first.  Once they die you can turn your attention to the real thing.  The illusionary drakota can be easily found because their health is significantly lower than their real counter-part.

The Death Fist Citadel: Assault Instance is only one groupable so you will have to break up into teams to get the last ring.  You will have to head from the sewers up to the top point where you will kill a named orc. 

With all of the rings in hand head to the Oracle Tower where you will use the globe in the top part of the tower to head to the Island of Refuge: Darathar's Flight. 

You can bypass all of the trash and simply pull Darathar if you get a good line of sight on him.  However if you want to do it the honest way you can fight the x2 and x4 mobs on the island to get to him. 

Darathar will heal at 75%, 50% and 25% to 100% health.  Once he does his final heal at 25% you can just burn him down.  Make sure to get under his belly to avoid his tail swipe attack.  After that you just have to watch for his AoE and you're pretty much set.

If you kill Darathar while he is green you should receive a hefty chunk of AA XP.  Heading back to Nagafen you will learn that he didn't really care if the egg got broken or not.  He only cared about it being out of his hands.  Your reward for this quest is a wrist item, prismatic weapon, title: Of The Shard, some xp and some coin.