Fire Emblem: Shadow Dragon/Chapter 20

Camus the Sable "It was General Ordwin, one of the Three Heroes of the War of Liberation, who put Grust on the map. His peerless knights tamed their neighbors the barbarians in the kingdom's infancy, securing its place as one of the greatest of the Seven Kingdoms. However, the current king, Ludwik, was weak-willed and easily cowed: Doluna had little trouble forcing him into an alliance. Now he had taken ill, even as Grust suffered its string of defeats at the hand of the League. The once mighty kingdom was poised to fall..."

Preparation
Beck works well to counter the enemy ballistae. Other than that, just take your other generic team. You may wish to use your master seal to promote units. Use the various stat boosts from last battle's chests.

When ready, start the map.

Begin
First turn, use Beck to get rid of the ballista. If you don't have him, move Shiida and any other flier away until you kill it. This is because the ballista has arrowspatte and most likely will critically damage your flier. Use Shiida's Wing Spear to defeat the generals in the vicinity.

Use an overpowered unit like Wolf to solo the west side. Equip him an Iron Sword and all four paladins will attack...and promptly all die. There are two ballistae randomly placed out there, killing them will solve a whole bunch of immediate problems.

Another immediate problem is the paladins to the north. They deal about 15 damage to some units and thus put some at risk of dying since there are four of them. When done, move Marth up north. Use the danger zone to position them out of range of the ballistae. Then, DO NOT move Marth or anyone that is with him.

By the time you find a way to defeat them, Wolf should have destroyed the ballistae. Now, randomly assorted reinforcements will appear along with a thief trying to destroy the village in the center. The reinforcements are relatively small.

Now, use Beck to destroy the ballista next to the castle. Hopefully you have one thunderbolt left. Automatically, Marth will decide to talk to Camus (note that this is implied and all we see is the dialogue below)

Boss
It isn't possible to recruit Camus, if you attack him he says: "With this lance, Gradivus, I am all but invincible. A pity you had to waste your life."

Camus uses the legendary lance and packs a punch. Eliminate him with a Ridersbane + Beck combo. When you kill him, he says: Nyna... Farewell....

You might not be able to get Camus, but you can recruit Lorenz, the general guarding the gate. You need either Marth or Shiida. The following is the conversation:

Before seizing the gate, check out the village to the south you might have missed with Marth. Get the Hammerene, a good staff for Lena only. Finally, seize the gate.

If you have less than 15 units here, you will go to the Gaiden chapter. See Gaiden chapters for more details.