If you work with the Minutemen...
You and Preston Garvey are sitting on one of the walls of the Castle, the two of you are enjoying a drink when you two notice a squad of gunners approaching the Castle, what do you do?

If you you're NOT with the Minutemen...
You and your group are passing by the caste when you see a group of raiders loading up on ammo and explosives while taking Psychobuff, what do you do?