This is mission 10 in the Path of War, in Stronghold 2.
After Matthew Steele decided to join Lord Barclay and Deveraux, the Hawk runs over the country to prepare taking the rule. Meanwhile, Steele and Barclay are scouting Lady Seren's abbey. Steele advises Barclay to launch a siege on the abbey to prevent the King from fleeing.
Lord Barclay will set up his encampment in the southwestern passage and brings archers and spearmen. You start in the southeast with numerous swordsmen, pikemen, archers, macemen, spearmen and laddermen, accompanying your lord.
Barclay suggests that he will keep up Seren's troops, so that you'll gain enough time to move in and kill Seren. Meanwhile, the lady sends out 10 mounted knights to distract your troops. They will move out to the west, flanking Barclay. He will attempt to set up some trebuchets but they are killed by the knights and arrows. The knights are very devastating in close combat, so hurrying is essential. It is up to you if you kill the knights or move in.
The knights will strike down Barclay's forces, then target you. You can spare the green soldiers' life however, if you gather all your troops in a circle and move slowly to Barclay's position. Set everyone on aggressive stance and have them fight the knights. Leave the archers back a bit, who will provide covering fire (useful against mounts). You'll lose some spearmen and macemen, but the knights will all die. You can even lure them to Barclay's siege camp, forcing his spearmen and archers to engage Seren's knights.
Regardless to the fact that the knights are dead or not, you should command your troops next to the cliff that covers your starting position. Now comes the hard part: the field in front of Seren's walls are littered with traps, which need to be cleared. So, your attack will be commenced in two waves. The first wave should consist cheaper troops: archers, macemen and spearmen. They have considerably little health and archers are far from outnumbering the defenders. Choose a wall section and send your troops under it. They will spring man traps and make archers to light pitch ditches, even a few killing pits. The most welcome fact is that rolling logs are triggered.
While the first wave is being sacrificed, send in your laddermen to their target. A few of them should have pushed their ladders against the walls. Without any delay, gather all your remaining troops in a column and scale the walls. Butcher your way through archers and pikemen until you get down to the campfire. There are some pitch ditches, but fire does little damage if you keep your troops moving by repeatedly clicking on Lady Seren. Don't bother fighting pikemen at the campfire, go for Lady Seren. Your armored men and the Lord should send Lady Seren to the almighty God she adored so much.
Lord Barclay gives a treaty document to the Bishop, who would usher him in. Suddenly, Steele intervenes and pulls out his sword, reminding Barclay to their agreement. After Barclay sees that he won't progress much, they make a new agreement: whichever of them presents the crown to the Bishop, becomes the King.