Race to the Rescue is the twentieth chapter of Drake's Fortune. With Elena captured by Roman and Navarro, Nate rushed back to the monastery to regroup with Sully and rescue her, and simultaneously stop them from taking El Dorado now that they knew its true location.
After escaping the bunker, Nate contacted Sully over his walkie-talkie, informing him that Roman and Navarro captured Elena. However, Sully was dealing with problems of his own, as he was pinned down by mercenaries in the monastery courtyard. Nate came to his partner's aid and helped him take down all of the mercenaries. Nate then explained to Sully that the El Dorado statue wiped out the entire Spanish colony and even killed the Germans, which Sully could not understand at first. However, since there was not much time, the two ventured inside the church. Once inside, they were faced with more mercenaries. After defeating them, they uncovered a secret passage underneath the altar.
After climbing out of the bunker, head past the radio tower and follow the path to return to the monastery. Upon entering, you will immediately spot two enemies to the right, but they will not be aware of you. Take them out, and then head for Sully's position. Here, you will find a Dragon Sniper, which you will need for the snipers using Desert-5s, that appear after you defeat the ones harassing Sully. One sniper will appear directly above you, followed by another on the other side of the plaza, to the left of the library. Take them down, watching for their line of sight, as the one above you has a good view of the immediate area.
The snipers will be shortly accompanied by another wave coming from the library, which flanks you from the left and right. They primarily use M4s and SAS-12s, but will be backed up by another mercenary wielding the M79 grenade launcher. Focus on him with the Dragon Sniper, and then clear the rest using the rifle, switching it with something else if possible.
Another guy with a laser sight will appear at a window in the tallest tower of the area. Shoot him, but also be on the lookout for a guy wielding an M79, standing on the balcony on the tower's left. Another smaller group of mercenaries will arrive, but they should not pose any trouble with their ranged support taken out. Once all of the enemies are defeated you and Sully will need to enter the church.
Upon entry, you will be faced with several more enemies, scattered about the sanctuary. Dash to the pillar to the left and take cover, then grab the Dragon Sniper and quickly snipe all five of the laser sight mercenaries. There will be two on the upper left rafters, two on the upper right, and the last appears from the secret gallery once the rest has been taken out. They will be accompanied by two soldiers wielding M79s, and one with a SAS-12. They pose no real risk just yet due to the thick cover you should be using. Letting the M79-wielders come closer to you will prove beneficial for the second wave as well.
Unless you have extra sniper ammo from the previous fight, this sniper only comes with five bullets, although you can find another with two more on a church pew on the right. Likely you will have used all the bullets on the snipers, so switch it with an M79. If you advance further down the church, another group of mercenaries will appear, from the left and right wings, using rifles and shotguns. If you let the soldiers using M79s advance far enough, you will have ample time to grab one and return to cover at the entrance, as you will need the extra distance to avoid the SAS-12 shotguns.
Once they have been shot down, a third and final wave will appear from your rear, so quickly switch cover to avoid being shot in the back. One sniper will be positioned on the second floor, so shoot him down first, and then handle the remainder that came from the entrance. Once all enemies are down, Sully will be at the front of the altar. This means you should head up there too, as a cutscene will trigger, leading to the next chapter "Gold and Bones".