How do I create a quest that doesn't take place in the prophet's hut?

I want to create a quest like this. For example, we arrive at a prophet's hut (or some other location), and a dialogue box appears, describing our conversation and the employer's offer, with the option to accept or decline the quest (OK or Cancel). Let's say our employer tells us to kill a peasant. We go to the peasant, and when we attack, another dialogue box pops up with the peasant offering to kill the prophet, and we have the option to choose whether to kill the peasant or fulfill his request.
I hope it's clear what I mean.