[ Register or Signin to view external links. ]
30 G

This quest is the Legion endgame quest and unlocks other legion quests, et tu brute and arizona killer.

The quick quest details are:
Kill Mr House
Befriend/Defeat the Boomers - by helping them you gain a water breather which becomes useful later on when entering Vault 34
Blow up the Brotherhood of steel
-- Return to Caesar to activate the Et Tu brute? quest
Here you have to cure Caesar's tumor depending on your skill there may be alternatives however I didn't have a high medicine so I had to get surgical equipment from New Vegas medical center and retrieve parts from an auto doc in vault 34.
Return to Caesar to cure him (you can kill him but this wasn't the path I took).

-- This Completes Et tu brute
-- Speak to Caesar to activate the Arizona killer quest
Meet up with cato
Prepare for the assassination
Let cato know you are ready
assassinate the target - completes Arizona Killer
get back to Caesar to complete render unto Caesar

Personal experiences with this quest

You can blow up the Brotherhood bunker by pickpocketing the three security keys from three main people in the Brotherhood, namely Elder McNamara, Head Paladin Hardin and Head Scribe Taggart. You can then get the self destruct terminal password from the console next to the self destruct console itself. Once you begin the sequence the brotherhood become hostile towards you so make sure you are ready to run or fight.

With regards to vault 34, it is heavily irradiated (1 rad/sec for the entire time you are in the vault) so be sure to bring plenty of rad-x and radaway, there is a safe with a ton of them inside the vault but this requires level 50 lockpick to open. The vault is also teaming with ghouls and glowing ones so bring decent weapons.
If you have the water breather given to you by the boomers bring it along as you need to travel under two flooded corridors to retrieve pass keys to get to the auto doc.

After reporting to cato he gives you an NCR uniform and goes to the dam, when you're ready put on the uniform as only the NCR rangers can see through this disguise and proceed to the dam yourself.
What I did:
I had a good sneak level when getting to Arizona Killer around 70 so this may not work for all but I simply sneaked pass the rangers to tell cato I was ready, I then went and hid behind a large structure directly across from the Hoover Dam visitor center where I was hidden from rangers but could see the platform your target stands upon.
I then sniped the target and got the hell out of there as quick as possible as the NCR become hostile, by standing here to snipe the only NCR member within gun range is the ranger patrolling in front of the visitor center entrance this made getting out of gun range and far enough away to fast travel pretty easy.

WARNING:: Change out of the NCR uniform before fast traveling back to the fort or all the Legion soldiers will attack you as soon as you get there