In the TV adaptation, Game of Thrones, in the third season in the seventh episode, Daenerys and her Unsullied are parked outside of Yunkai. The messenger from the city comes to offer them gold and ships if they are willing to go away.
Alas, the mother of dragons cannot see people in chains, so she decides to put an unreasonable ultimatum so she will destroy Yunkai.
The ambassador, in return, says that they have friends who will put her army to death with great pleasure. After he leaves, Daenerys speaks with Ser Mormont about these "friends". She asks who they might be, and he says that he doesn't know. Her reply is for him to find out.
How? How would he find out? Would he knock on the city doors and ask people who are the mercenaries kept on retainer by the city leaders? Will he take out his smartphone and search on Google (I bet there's reasonable reception nearby such a glorious city)? Or in a classic Mel Brooks moment, he'll take out the script and search for the answer in the script?
Okay, all the above are fairly preposterous. But it serves to illustrate the point. It doesn't seem reasonable that he can "find out" in any way that doesn't involve engaging in war with the mercenaries to begin with...
Can anyone give a plausible explanation as to how he found out the answer without resorting to the above options?