I Put a Spell on You

 is a quest in Fallout: New Vegas.

Quick walkthrough
The last step of this quest is currently broken. Even if you sneak onto the train car by jumping onto the railing and hugging the side then disarm the bomb, it explodes anyway if you trigger its departure. Even if you successfully disarm the bomb and don't cause the train to depart and explode (despite just having disarmed it), you are given no conversation option to report your success to Hsu. You can, however, ask him for help with Bitter Springs after disarming the bomb, despite being unable to complete the quest. However, if you are able to pickpocket the code from the spy, you will have the option to input the code, and remove the bomb. The quest then updates and instructs you to Hsu.

you still aren't able to complete the mission though as there is no dialogue option for it.