By The King’s Will is divided in several parts, based on the story you tell to Vernon. The quest also reveals the events that occurred before your incarceration.
To begin this quest, speak to Vernon Roche, and select The morning, the King summoned me in the dialogue box.
Day of the Assault Dawn
You wake up in your tent and you see Triss Merigold near you. Suddenly a Temerian soldier interrupts both of you and you are asked to meet King Foltest.
After a short dialogue with Triss you find out that even if you dont agree with Foltests war, you must obey his orders, and help him defeat the La Valettes. Pay close attention to the dialogue with Triss because she will ask you about your dream, called The Wild Hunt.
After you talk to Triss, tell her that you must go, and then exit the tent. Your next objective is to find Foltest in the Temerian Camp.
While exploring the camp, there are several points of interest you should focus on. The first one is a tent on the right side of the path that takes you down the hill. You will see a Temerian Recruit standing in front of the tent.
Tell him that you kill the cockatrice (in the first Witcher game) and that you want your reward. Then ask him about the assassin.
Next, look for some bald soldiers near the recruits tent, and find Newboy. Talk to him to start Melitele’s Heart side-quest.
After you start Meliteles Heart quest, continue to explore the camp and make sure you pick up all herbs and items inside the crates. If you check the northern side of the camp, you will find Strongarm and behind the tents, a soldier.
If you need additional orens play some dice poker with the soldier. If you roll five-of-a-kind you will unlock the Poker! achievement.
Next, win an arm wrestling match for the Gambler achievement and brew five potions to unlock the Apprentice achievement.
After you complete these tasks, meet King Foltest up on the hill. Near him you will see Shilard Fitz-Oesterlen, the Nilfgaardian ambassador. Foltest wants you to follow him and help him lead the attack.
Stay near Foltest and pay close attention to his dialogue with Shilard Fitz-Oesterlen. When Foltest asks you to help him fire the ballista, make sure you aim for the soldier standing on the left side of the tower. You will see him moving on the wall.
The consequence of this action can be observed later in the game, and you will unlock the Eagle Eye achievement, for killing Count Etcheverry.
Now, enter the siege tower and continue to follow Foltest until you reach the top. While Foltest encourages his soldiers, your story is interrupted by Roche. Continue to tell Roche what happened, and focus on the assault.
Day of the Assault Morning
Your first goal is to protect Foltest and fight by his side. Since this is the first combat sequence in the game, you wont have any problems in defeating La Valettes soldiers.
Practice your combat skills on these weak opponents and clear the walls. The Barricade main quest starts now.