Note: Both Ricardo and Wendel are locked in a room above of your starting location.
First of all, this is an inside chapter, this means that all your mounted units will be dismounted and can use only swords.
Now, you need to open those chests before the enemy, so ignore Wendel and Ricardo for now, and advance as fast as possible.
You know how to beat that armor knight, so just lure him with Marth and his Rapier.
It looks like there is no way to reach the northern chest before that thief, right? Well, just use Rena’s warp staff to move a character there and block the chest. If other thieves open chests, just kill them and they will drop the item they stole.
You must know how to kill all the enemies. Just lure them and finish them quickly. But be careful with the enemy mage. You have to do it fast and kill all the thieves. If you can’t reach them, the character that you warped to the northern chest should block their escape route.
The rest of your team should advance towards the boss, slowly luring all the enemies and healing if necessary.
Once you have all the treasure, send Maric and Julian to the room where Ricardo and Wendel are caught and recruit them.
The boss has good defense, but he is nothing against Maric’s magic.
If you got the Angelic Robe, I suggest giving it to Marth.
After you seize the throne, Princess Nina will give you the Fire Emblem, with it, Marth can open chests.