Lord Morgan, Favoured of Slaanesh, was displeased. He had just
received a report that a small army of Bretonnians was bearing down on
his fortress. From his throne of horrifically mutated small dogs, he
pointed to Jiros, his "assistant":
        "Tell Petar to get his b1tch @ss down here right now."
        Petar duly arrived. "You called, Lord?"
        "Yes. We will shortly be besieged by the Bretonnians. I want you
to go to Mr. Morden's fortress and send some troops down here, the
advance Bretonnian scouts are all over the place.
        "Right away, Lord."
        Petar mounted his Steed of Slaanesh, summoned half-a-dozen of
his most trusted followers and left the building.

BRETONNIA
*********
        Jaron Caprion, leader of the somewhat mysteriously-named Patrol
Sigma Alpha, leapt from his seat upon hearing that some mounted figures
had left the fortress.
        "Summon my Knights Errant! Find me some infantry! We must stop
them before they can send for help!"
        Bugle calls sounded as the Bretonnians broke camp, ready to
interdict the movement of the Chaos forces.

Jaron Caprion, Grail Knight Hero with Knightly Equipment
The Errant de Caprion, 5 Knights Errant
The Bushwhackers (10 squires with longbows)
Jaron's Men (10 archers with longbows)
Jaron's Other Men (10 archers with longbows)

CHAOS
*****
        Petar, leader of the Patrol, motioned toward the Bretonnians
from the back of his galloping steed.
        "We must break through! Avoid the Knights! Those squires are
guarding a pass, we are sure to break them on the charge!"
        A volley of arrows, 50 yards out of range, swept from the sky.
Petar increased speed, leaving his Knights behind as he felt the Favour
of Slaanesh on him.

Petar, Chaos Hero of Slaanesh (Chaos Armour, Steed of Slaanesh, Lance,
Shield)
2 Chaos Knights (Chaos Armour, Shield, Lance, Chaos Steed)
4 Marauder Horsemen (Flails, Light Armour, Warhorses)

[*[ In this battle, the Chaos force, acting as independant models, must
leave the board through a 12" wide area on the other side. They have 1-2
messengers, one a character and one a rank and file model, one of which
must get through. The Bretonnians are not in favour of this, and want it
stopped. ]*]

Turn 1: Chaos
*************
Petar galloped forward, ending up far from the Knights Errant and just
beside an Arrowhead of archers, who shied away from his Steed of
Slaanesh. His henchmen split into two groups consisting of a Chaos
Knight and two Marauder Horsemen, who also galloped toward the
Bretonnians.

Turn 1: Bretonnia
*****************
The Knights Errant, wildly out of place, repositioned themselves to
charge next turn. The archers let loose with arrows, cutting a Marauder
from his saddle (despite rolling 5 1's to hit).

Turn 2: Chaos
*************
Petar swerved round the Knights Errant, moving over to charge the
Squires that were blocking his path of exit. His (depleted) followers
moved to the rear of the Knights Errant, the Chaos Knights ready to
charge.

Turn 2: Bretonnia
*****************
The Knights Errant swerved again, churning the ground beneath their
hooves as they turned their snorting horses to face the Chaos Knights.
More arrows took care of 2 Marauders.

Turn 3: Chaos
*************
Petar and his two Chaos Knights charged the Squires. The last Marauder
bought time for them by moving to the rear of the Knights Errant. 6
Squires died under sharp lances and broke, fleeing off the board. Petar
and the Knights followed. They had broken through!

RESULT
******
The siege would end more quickly (+1 to the roll to see exactly when).
Also, Chaos could (and did) attempt to bring reinforcements to give them
a hand.

Part II: Reinforcements have arrived! is next.