Index: ps/trunk/binaries/data/mods/public/simulation/ai/petra/army.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/petra/army.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/petra/army.js
@@ -89,6 +89,9 @@
 /** adds or remove the strength of the entity either to the enemy or to our units. */
 m.Army.prototype.evaluateStrength = function (ent, isOwn, remove)
 {
+	if (!ent)
+		return;
+
 	let entStrength;
 	if (ent.hasClass("Structure"))
 	{
@@ -279,7 +282,7 @@
 m.Army.prototype.clear = function (gameState)
 {
 	while (this.foeEntities.length > 0)
-		this.removeFoe(gameState,this.foeEntities[0]);
+		this.removeFoe(gameState, this.foeEntities[0]);
 
 	// Go back to our territory, using the nearest (defensive if any) structure.
 	let armyPos = [0, 0];
Index: ps/trunk/binaries/data/mods/public/simulation/ai/petra/attackManager.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/petra/attackManager.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/petra/attackManager.js
@@ -503,6 +503,54 @@
 	this.raidNumber++;
 };
 
+/**
+ * Response to the capture of one of our structure:
+ * transform all defense armies around into a new attack army and target this structure
+ */
+m.AttackManager.prototype.counterAttack = function(gameState, ent, range=150)
+{
+	if (!ent || !ent.position())
+		return false;
+	let pos = ent.position();
+	let attackType = "Attack";
+	let attackPlan = new m.AttackPlan(gameState, this.Config, this.totalNumber, attackType);
+	if (attackPlan.failed)
+		return false;
+	this.totalNumber++;
+	attackPlan.init(gameState);
+	this.startedAttacks[attackType].push(attackPlan);
+
+	for (let i = 0; i < gameState.ai.HQ.defenseManager.armies.length; ++i)
+	{
+		let army = gameState.ai.HQ.defenseManager.armies[i];
+		army.recalculatePosition(gameState);
+		if (API3.SquareVectorDistance(pos, army.foePosition) > range*range)
+			continue;
+		while (army.ownEntities.length > 0)
+		{
+			let unitId = army.ownEntities[0];
+			army.removeOwn(gameState, unitId);
+			let unit = gameState.getEntityById(unitId);
+			if (unit && attackPlan.isAvailableUnit(gameState, unit))
+			{
+				unit.setMetadata(PlayerID, "plan", attackPlan.name);
+				attackPlan.unitCollection.updateEnt(unit);
+			}
+		}
+		gameState.ai.HQ.defenseManager.armies.splice(i--, 1);
+	}
+	if (!attackPlan.unitCollection.hasEntities())
+	{
+		attackPlan.Abort(gameState);
+		return false;
+	}
+	attackPlan.targetPlayer = ent.owner();
+	attackPlan.targetPos = pos;
+	attackPlan.target = ent;
+	attackPlan.state = "arrived";
+	return true;
+};
+
 m.AttackManager.prototype.Serialize = function()
 {
 	let properties = {
Index: ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
===================================================================
--- ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
+++ ps/trunk/binaries/data/mods/public/simulation/ai/petra/headquarters.js
@@ -213,6 +213,14 @@
 
 	for (let evt of events.OwnershipChanged)   // capture events
 	{
+		if (gameState.isPlayerMutualAlly(evt.from) && evt.to > 0)
+		{
+			let ent = gameState.getEntityById(evt.entity);
+			if (ent && ent.hasClass("CivCentre")) // one of our cc has been captured
+				this.attackManager.counterAttack(gameState, ent);
+			continue;
+		}
+
 		if (evt.to !== PlayerID)
 			continue;
 		let ent = gameState.getEntityById(evt.entity);