He also orders you to take any Swedish lord prisoner. After Warsaw it taken, the King makes you a Polish lord and grants you a very poor (usually recently looted) village. There are time periods when the letter does not work and all lords decline, telling they have no time - simply wait for 1-2 day and try again. You can show the letter to any Polish lord and he will usually agree to follow you for 1-2 days.

It is strongly garrisoned (around 300 troops), so to make it easier, the King gives you a letter with an order to all Polish lords to follow you. Jan Kasimir will then tell you to take back Warsaw.Warning: bandits are actually quite large party of regular Swedish troops. When you are back to Jan Kasimir, he tells you to stop Swedish bandits from looting Chenstokhova.Warning: it is recommended to make a backup save at this stage in case a bug happens when you get to step 9 below. Other nations will most probably take an opportunity and grab few Polish settlements. Meanwhile Warsaw and Krakov become Swedish and Swedish Armies appear.Hand him to Jan Kasimir, he tells you to come a week later, after the prisoner is interrogated. You need to take prisoner any Swedish unit - easiest way is to intercept a small patrolling party and kill one of them with a blunt weapon like mace (don't forget that horses and firearms in melee also deal blunt damage). King Jan Kasimir will ask you to capture a Swedish soldier. When the King reads it, you will find out that the letter warns of a Swedish invasion.Any Polish lord when asked will give you a letter to be delivered to King Jan Kasimir.Talk to Zagloba and he will advise you to find any Polish lord and ask him for a special mission. Find Colonel Zagloba and invite him to your party.Ask Polish lords 'Perhaps you can tell me of a way to help the Polish Commonwealth?' until one tells you to make friends with Colonel Zagloba, who must be in a tavern.You must accept if you wish to start the main quest. He tells you that Poland is in danger and asks your help.

Ask a Polish lord 'Tell me - what news have we from the Polish Commonwealth?'.

Achieve at least +10 relations with Poland.

Mount and blade the deluge