Birds of a Feather

 is a quest in Fallout: New Vegas.

Quick walkthrough
This quest can be activated after completing several jobs for the Van Graffs in Freeside. To start it talk to Gloria inside behind the counter. She will say Jean-Baptiste has a job for you. Speak to him and he will task you with bringing Rose of Sharon Cassidy to him.

She will be down at Mojave Outpost unless you have already gotten her as a companion via another quest. To get her to follow you, you will have had to complete the quest 'Heartache by the Number'. When you bring her back to him he will reveal his purpose is to kill her. From here you can choose to let him kill her, or become hostile by saying "Shoot her and you'll be sorry" If you choose this method you will have to kill all the guards inside the Silver Rush. Alternatively you can let her die and you will be paid 350 caps. Or, if you have the Terrifying Presence, you can convince Jean-Baptiste to hold on.

It is possible to kill Jean-Baptise and get away with it if you have already started this quest and want to purposfully fail it to save Cass. You will fail the quest but if you want to save Cass and NOT fight the guards you will need to use the Stealth Boy, sneak up and pickpocket Jean and place a grenade and let him explode. You will have to back up in the nearest corner or space available to not get detected by the guards but it is fully possible to escape from there without fighting everyone.

Detailed walkthrough
1. First you will have to guard the front door. A series of 4 NPCs will come up to you, and you must remember to allow no drunks and everyone must be searched before going in. Passing a speech check on the third customer results in being paid a bonus on top of the job's normal pay (65 Speech). The fourth NPC will be carrying a bomb. If you choose to let him in, he will blow up the entire store (and any items inside of the store as well), failing the quest.

2. You will need to deliver a package to a man a bit east of New Vegas. With a high speech check you can get 200 caps from the man.

3. You will need to bring back Rose of Sharon Cassidy to the Silver Rush to be killed. If you bring her to Jean-Baptiste and allow her to die while in dialogue, you will lose her as a companion and fail her companion quest if you have not already completed it. However you will succeed at this quest and get a large sum of caps as a reward. (If you have a companion with you at this time you will need to split with him/her to allow Cass to follow you.)

If you end up killing Cass instead of recruiting her, the journal will update to tell you to 'Let Jean-Baptiste know that the Cassidy girl is dead'. Upon returning to him, you will still be rewarded and the quest will end as normal.

You can also choose to resist her death. This results in a fairly difficult gunfight, especially if you're low level. As soon as you threat Jean-Baptiste he'll run for the Plasma Caster on the left side of the display table. This weapon will deal you massive amounts of damage to you and your companions, in addition, every single Van Graff Thug will turn hostile on you. Your best bet is to tell Cassidy and any companions you might have with you to wait in the corridor that leads to the restrooms and quickly steal the Plasma Caster before Jean-Baptiste or any thug picks it up to use it against you. Then join your companions in the corridor and deal with the Van Graffs one by one with the Plasma Caster (Don't forget that Simon, the guard outside, will also be hostile once you exit the building). You can also isolate Jean-Baptiste and focus him down first, but he has very high DTS. All the guards and his sister do not have as much, so you might need to kill them before moving on to him. Doing this will result in you failing this quest and no EXP reward, however you will be able to complete Cassidy's quest for that reward and loot all the equipment in the Silver Rush shop which can be kept for combat use or exchanged for a huge amount of caps. Or, you could complete her quest first and then lead her here to her death and complete both.
 * You can make the fight easier (to the point of being nearly impossible to lose) by pickpocketing the ammo off of Gloria and Jean and performing sneak-silenced kills on all the "Van Graff thugs" inside before starting the conversation. (And steal the various guns and ammo lying around the place as well, of course).  Without any weapons, or any nearby to grab, the two Van Graff siblings will attempt to punch you and your party to death, and even for a lower level character, provide little challenge.

Normally you are forced to either let Cassidy die or fight the Van Graffs as soon as you initiate dialogue with Jean-Baptise, but if you have the Terrifying Presence perk, you can exit the dialogue and take more time before coming to a final decision on how to handle the situation.

4. If you choose to just let Jean-Baptiste kill Cass, then Gloria will ask you to help her with one more thing. The reward for helping her is 1000 caps and the Van Graff Combat armor. What you actually have to do is kill Caesar's troops in the Abandoned Warehouse.

(5. Code workaround). If you want to finish this quest, without letting Cassidy be killed by Jean-Baptise. Enter in the console "setstage 124123 100" This will complete the "Birds of a Feather" quest, resulting in 1000Caps and NCR and Freeside fame. Jean-Baptise still wants to kill Cassidy, so don't talk to him with her as companion.

Bugs

 * If you pickpocket Jean Baptiste's ammo, and carry through with allowing him to execute Cass, the game will become stuck when he goes to fire the killing blow. He'll be unable to, and simply stand there... and you'll be stuck in place.  To remedy this, reverse pickpocket a microfusion cell onto him and leave the Silver Rush (so that he re-equips his laser rifle).  When you re-enter, he should have his laser rifle equipped and be able to kill Cass.


 * If you have killed the Van Graff thugs (sneak, silent kills to prevent the Van Graffs from being hostile), they'll still zone into the Abandoned warehouse that's part of the final task for this quest. They zoned in dead for me, and a couple of them were partially/mostly stuck in the floor.


 * It is possible to steal from the footlocker next to Simon, the guard outside. Besides finding some decent ammo and weapons, you can also get the Van Graff Armor. However, once you steal it, it becomes stuck in your inventory, marked as a quest item. Even when Simon gives you another Van Graff armor as part of the quest to guard the door, the armor stays stuck in your inventory. Because the armour is a quest item it doesn't actually weigh anything even though it says it weighs 25. However if you complete this quest and receive another set of the armor they will stack, removing the quest item tag from the original stolen armor and giving it back it's weight.


 * If you choose to guard the door with Simon there is a potential bug. After 4 npcs, there will be a special NPC who will chat with Simon.  If you aim your weapon at him he will stop talking to Simon but permanently stand outside of the Silver Rush.  If you enter the Silver Rush, you can take the next quest to deliver a package, but once you leave the outside post, Simon will attack you as a theif of the Van graff weapons and and armor.  This bug is compounded by the autosave, and can permanently deny you relation with the Van Graff.
 * This bug may be bypass by the following.
 * Open Console with Simon on the screen, Then click him.
 * Enter StartConversation 001185d4 VFSSimonCallsItADay
 * If You wish to hear the dialog close the console and wait for him to finish, after he is done or you may just repeat the previous 2 steps again this will Trigger a dialog about him taking your weapons back and he will walk inside


 * When guarding the door if you talk to a customer before they talk to you the customer will talk to you again right after. (allowing for double xp on the speech chat options


 * Also during the door guard section of the quest, if the Courier denies the fourth customer entry he will turn hostile. If the Courier deals the finishing blow in the resulting fight, Simon may freeze in place. He is supposed to walk over to the corpse, but will instead stay next to the door with his weapon out and become unresponsive to dialogue. He will stand there staring at the Courier, and will never speak the dialogue that triggers the fifth customer. He will, however, become hostile if you go far away from the Silver Rush, like normal. The easiest way to avoid this is to let Simon kill the fourth customer by himself - he's more than capable.


 * If you have an NCR trooper following you (by using the NCR emergency broadcast) he or she will shoot the "Strange Man" you deliver the package to in the second leg of the quest. This is due to the man being a part of Caesar's Legion.


 * In the second leg of the quest when approaching the strange man, sometimes he will start fleeing when no enemy is present (for me he ran east after a while we ran into an area full of young deathclaws and blind deathclaws which killed him and ended the quest). - One person has found that by unequipping all armour and weapons, and 'holstering' the fists, he will not flee, although it is unknown what makes him run


 * If you have an NCR trooper following you (by using the NCR emergency broadcast) then the Caesar's Legion will attack him and Gloria won't give you the "signal" meaning you will be permanently stuck in the warehouse, unable to move.


 * You will not gain any Infamy with Caesar's Legion as long as you let the NCR and Van Graffs kill everyone and fire no shots at Legion soldiers in the Abandoned Warehouse. But you are free to kill the three unconscious Legion soldiers with no Infamy gained.


 * There's a chance that after you get the guard job and you exit the store, your companion will stand between you and Simon (in front of the door). As soon as you move to your post, you can't move again until Simon gives you the gear. However, if your companion stands between Simon and you, Simon will get stuck. You won't be able to move to get your companion to follow you. You'll have to reload.


 * If you decide to resist Cassidy's execution all the Van Graffs will turn hostile on you. If this occurs they'll run behind the show desk and grab any special weapon they can, this can lead to a massive obstruction due the small space that will trap your foes (sometimes all of them, including Jean-Baptiste) into a convulsing human jam unable to move and properly engage you. If that happens you can easily take them down one by one or use explosives against them. Though that may push the survivors free.


 * You can hire multiple Freeside bodyguards to accompany you into final part of the quest where you surprise the Legion in the warehouse and attack with the Van Graff's and NCR in a sting.


 * While walking to the drop location, the map marker tells you to enter Isaac's house and exit out the back door and continue on. I was standing outside of Freeside's east gate when I selected this quest, maybe thats why.