This is mission 9, in the Path of War, in Stronghold 2.
Sir William finally appears in front of the King. He would start speaking, but the King interrupts him, stating that he would make a very poor traitor. The bond of trust between them is restored and the King plans a three-front attack on Lord Barclay's castle, to remove the landlord from his seat of power.
Sir William starts in the north of the map, the King in the east and you (as Steele) in the south. Your troops are much spread out, some of them within range of a tower ballista. Reassemble your troops on the small peninsula to get out of range, but don't move trebuchets. Meanwhile, William starts his own attack with trebuchets and catapults, marching his force. He will be busy breaking through Barclay's first lines for a long time.
In the meantime, the clan Mcloud turns up with the Bull on the fore to kill the King. The royal forces are somewhat surprised at the attack, but they will deflect it with ease, killing Angus eventually. The Bull will make a promise for vengeance, although his troops never come back. After it, he starts the siege. Although he constructs a cat and tries to soften up Barclay's defenders, he won't be able to get in as he doesn't have laddermen or siege equipment. He'll depend on you or William's laddermen.
You should start by taking your 4 fire ballistae with the lonely cat and roll them to the horn of the cliff facing Barclay's rightmost tower ballista. Take it and the archers around it out, then repeat this process with the three mangonels. Leave the left ballista alone. March your catapults and some spearmen to the bridge connecting the mainland and the plains you started on. Damage the walls built on the top of the hill to remove rolling logs. Don't tear them down or else the left-out ballista will relentlessly target you.
Your spearmen should be sent ahead. On the steep two hidden man traps are placed - you don't want to lose your siege equipment on them. Back up with your ballistae and kill archers on the first gatehouse and walls just ahead of you. The entire section can be torn down (except for the aforementioned one on the hill). Bring all troops except the trebuchets to your assault position. Choose a wall section and send spearmen and archers to the fore, triggering a small path of traps. Target troops in the round tower and on the wall a bit further from that position.
After the first gatehouseEdit
Sir William will have lost most of his men now. However, he will keep sending swarms of laddermen to push ladders against Barclay's walls and pins down ballistae and mangonels. If he had captured the western gatehouse, the King with his swordsmen and pikemen should start breaking in. His troops will be distracted and destroyed, but you will be able to do it in your own.
Move some spearmen and archers under that wall to trigger two killing pits. When everything is clear, send your two trebuchets there and start bombarding the two great towers in front of Barclay's fortress. This will take some time, so speed things up. Your main goal is to knock the tower with the mangonel down, the other could be left alone. Tear the main gatehouse down, if Barclay's mangonel forgot to, with the trebuchets. Create a hole in the wall you have your troops at, and move your remaining spearmen and archers to the east to trigger more man traps and killing pits.
The final chargeEdit
Get under the cliff, then march your knights, lord and macemen (and leftover archers and spearmen) in one big group to Barclay's keep. Send your other troops after them. You'll encounter high areas of pitch lit up and killing pits, but your troops will eventually make it to the fortress. Have the mounted troops dismount and don't fight with Barclay's swordsmen. Your soldiers will fall one by one to Barclay's mighty hammer, but he should surrender in no time!
Congratulations on completing the Blue Path of the campaign!
Lord Barclay collapses to Sir William, who boasts on their final victory. Later the King's staff is seen in a village, where the treacherous Edwin and the cruel Barclay is taken away in a cart, while the mass laughs and throws vegetables at them.