Heartache by the Number

 is a quest in Fallout: New Vegas.

Quick walkthrough
Talk to Alice McLafferty in the Crimson Caravan main Office, ask for work. After telling you there's no caravan work she'll ask you to deliver a holotape to Doctor Thomas Hilderm. He can be found inside the Terminal at Camp McCarran, just east of New Vegas. He will tell you to return to Alice.

1. Cass is drowning her sorrows at the Mojave Outpost. Her advice? Go work for the Crimson Caravan. 2. Pitch in at the Crimson Caravan company if you're looking for caravan work. 3. Alice McLafferty will give you a Holotape to deliver to Doctor Thomas Hildern. He's located inside the main building of Camp McCarran, on the ground floor on the left. 4. Return to Alice McLafferty and let her know you've delivered the invoice. 5. Return to Cass and see if you can get her to part with the title for Cassidy Caravans. 6. Pay your respects with Cass at her caravan's grave. 7. Investigate the wreckage of the Griffin Wares caravan with Cass. 8. Track down Durable Dann's missing caravan with Cass. 9. Cass will give you an option for the next part of the quest to a) find evidence to incriminate Crimson Caravans and the Van Graffs, or b) Kill Alice McLafferty and Gloria Van Graff. 10. 11. 12. When the questline is completed, Cass will receive a) the Calm Heart perk, or b) the Hand of Vengeance perk. Calm Heart gives Cass +50 HP, while Hand of Vengeance gives Cass a damage boost with Guns (confirmed, (15%, unsure)
 * Option a) Investigate the Crimson Caravan for reasons behind the attack. The evidence is located inside a locked safe in McLafferty's office, next to her desk.
 * Option b) Assassinate McLafferty.
 * Option a) Investigate the Silver Rush in Freeside for evidence on the Van Graffs' guilt. The evidence is located inside a Hard locked safe behind a Hard locked door. There is also a Hard computer terminal to unlock the safe.
 * Option b) Assassinate Gloria Van Graff
 * Option a) Take the evidence of the Caravan attacks to Jackson at the Mojave Outpost.
 * Option b) Cass will gloat about the joy of killing her enemies, simply hear her out and the quest is over.

Hint: If you first follow option A above, you can then pursue option B, which, upon completion, will give Cass both perks.

Peaceful Solution
When trying to get the data from the Van Graffs there are two ways that you can go about this:

a.) Talk to Gloria Van Graff to start the quest Birds of a Feather, during the first part of the quest where you guard the front door of the shop four men will come up to you wanting to come into the shop. The fourth man will tell you how he's looking to replace his gun. Let him in and he will suicide bomb the inside of the shop killing everyone inside. Simon will run inside and will turn hostile towards you for destroying his place of work. There's also some pretty good loot by doing this and you keep the Van Graff combat armor and Van Graff Laser rifle. Note: Doing this will make it where you don't need to prove that they were conspiring with each other.

b.) To get the note proving the Van Graff's guilt out of their safe non-violently, sneak behind Simon (the guard at the door) and pickpocket his office key. You have to stay as far away from Simon while getting behind him otherwise he will continue facing you as you walk around him. Gloria Van Graff also has a key to the office that can be pickpocketed. It may also help to have started the Birds of a Feather quest so they are more friendly towards you. The safe and computer both require a 75 skill check in their respective area. Note that bringing Rose of Sharon Cassidy and talking to Jean-Baptiste Cutting will result in him killing her (Unless you have the Terrifying Presence perk). Note: If you pickpocket Simon and fail but you have stolen all the loot in the black box next to him he will take those items off you as well so save the game first.

After showing the Van Graff letter to Rose of Sharon Cassidy, you'll have to get into the Crimson Caravan safe for the other letter. The safe requires a 50 skill check, otherwise you can pickpocket the key from Alice McLafferty. Pickpocketing Alice McLafferty is going to be very difficult if your sneak is low, but using a Stealth Boy works wonders. Retrieve the letter from the safe and show it to Rose of Sharon Cassidy. If you kill Alice McLafferty to get her key, Rose of Sharon Cassidy will only want to kill the Van Graffs and this will most likely end up with Rose of Sharon Cassidy dying as well as yourself.

Violent Solution
The Van Graffs are heavily armed and have good armor. Going into the Silver Rush and winning the ensuing gun battle may be very difficult.

However, if the Courier kills Simon first, four of the Van Graff thugs will come outside to do battle with the courier. By using a weapon such as a sniper rifle, they can be eliminated without too much difficulty. Upon entering the building, the Courier will be faced by one thug, Jean-Baptiste Cutting, and Gloria Van Graff. If the Courier takes out Cutting first, then the other two are relatively easy to dispose of.

It is also possible to kill all of the Van Graffs inside the shop by killing Jean-Baptiste Cutting first, and then standing behind Gloria Van Graff to keep the thugs from firing on you. They will all run behind the counter to try to take a shot at you and you can kill them one at a time.

an extremely easy way to kill the Van Graffs is to ask Gloria for a job. When you are given the job of guard at the door, allow the customer with the merchant outfit to enter without checking him and he'll blow the place with a powerful explosive, killing everyone inside. Cass will react just as if you killed the Van graffs yourself.

Bugs

 * If the PC accepts Can You Find it in Your Heart? and You Can Depend on Me before talking to Cass this quest will glitch so that the PC has "Clear the roads for Jackson..." and "(Optional) "Remove" Jackson as an obstacle..." completed and cannot progress any further.Solution Needed (PS3 and Xbox 360 Confirmed)
 * Solution: If she becomes your follower, just use the Talk To option and she will ask to go pay her respects at her caravan's grave. (PC,Xbox 360 and PS3 Confirmed)
 * Alternative Solution: If you previously killed the Van Graffs for the Brotherhood of Steel, but still want to finish the quest in peaceful way (and to obtain Calm Heart Perk for Cass), get both pieces of contract from VanGraffs and McLafferty, then bring the proof to Ranger Jackson, the quest will be completed after you speak to Cass.
 * Alternative Solution: Further to the situation described by the alternative solution noted above for the PC, it's worth noting that the quest log within the Pip-Boy will still show the waypoint to complete the quest as "Settling the score" with Alice McLafferty. If this happens, killing McLafferty will not end the quest, you will gain Infamy with the NCR - there will be no dialogue option to end the quest either before shooting her. The trick is to take the affore mentioned evidence to Ranger Jackson at the Mojave Outpost and the quest will end granting the Calm Heart Perk to Cass.


 * The continuity of this quest will be very confusing if you previously killed the Van Graffs for the Brotherhood of Steel or for other reasons. Upon first meeting Cass, she will tell you that she's glad the Van Graffs have been dealt with and that all that's left is to kill McLafferty.  The game will trigger the "Kill McLafferty" leg of the quest, even though neither you, nor Cass herself, have any idea why she should be killed.
 * A glitch is involved due to the above event. If action is taken upon the Van Graffs before the quest, then the murder of McLafferty will not end the quest, nor change options. It will appear to be uncompleteable since the marker is still shown at her body. However, after a longer wait you can talk to Cass, thus ending the quest.
 * Jean-Baptiste may have bolstered his rifle meaning he does not shoot Cass, just stares her in the face. If this happens, kill cass outside of the silver rush before talking to him. NOTE: You may need to be on hardcore to kill this companion so a brief setting change may be necessary.
 * There is a glitch when trying to give the package to Hildern if you have already completed the There Stands the Grass quest. He will not open a dialogue option for handing him the package meaning you can't finish the quest.


 * When accessing the Van Graffs safe and terminal the graphics didn't show up but the noise was made for each. A way around this is to try the safe and use the vibrations of the controller to determine if the bobby pin is in the right area.


 * If you enter the Silver Rush and leave before the scene between the Van Graffs and the individuals that owe them money is complete the characters will remain frozen when you return. If you are trying to gather evidence against McLafferty and the Van Graffs, this will leave you unable to enter the Silver Rush to find the evidence without triggering them to attack you.


 * Upon choosing to "find evidence" for cass, then killing the Van Graffs anyway, recieving the note in the Van Graffs' safe does not let the courier finish the quest through a non-violent manner. The Courier can still give the evidence to Major Jackson, although this yields nothing. The only way to complete the quest is to Kill Alice too.


 * While attempting to complete non violently, and bringing Cass to see Jean-Baptiste he will attempt to kill her. If you tell him he will be sorry, they turn hostile towards you. If the courier and Cass survive the ensuing fight the letter will not be in the safe, and the terminal will not be accessible. Not sure what causes this. The only way to complete is to kill McLafferty.


 * If you kill the Van Graffs by bringing Cass to see Jean-Baptiste (And locking yourself into the "kill" chain) it seems you can kill McLafferty by simply taking Cass in your party to see McLafferty, then "releasing" Cass. As soon as she is released, she guns down McLafferty, none of the NPC's fire on her, or you. She then opens a dialog with you, talks the end of the quest through, then continues walking off back to her waiting point. No Karma is lost


 * There appears to be a bug by which the quest cannot be completed if you tell Cass to wait while attempting to sneak around to recover quest evidence. Presenting the evidence to Jackson does not resolve the quest, although this may be because Cass isn't around to talk to (she appears to have not reliably default to the starting location (Mojave) or Lucky 38 like most other followers)

Behind the Scenes
This is one of many quests that are named after songs that can be heard on the radio, in this case the Guy Mitchell song Heartaches by the Number, which is broadcast in-game on Radio New Vegas.