20% chance: Mercenary佣兵 company hired by the nobles offers to switch sides for 50% of your contract reward. If you pay, they'll help you in battle and if you refuse you'll have to fight them in addition to the noble forces.
20% chance: After the battle you will have to fight another army of northerners. You will have an option to make a stand in the holy site, attack them in the open or run away which will result in failing the contract.