This scenario takes place in a ruined port (#1) which is controlled by the enemy soldiers. Enter the pier and approach the old man. Follow him to the gate, picking up the supply crates (#2) with a Gravity Gun (don't enter the water, some deadly fish in there).
Head up (#3). In a moment you'll see the first enemy soldiers (#4). Kill them. Remember that you'll be attacked from above, so keep an eye on your surroundings. Use your Colt to eliminate distant targets.
When you are up you'll see wooden stairs (#5). When you try to use them, they will be destroyed. Head down and jump towards the supply crate and another stone platform. Go forth, eliminating all the enemies. After a short walk you'll see the enemy soldiers dropping from above. Kill both them and the enemies who are on the lower level. Jump to the other platform (#6) and go up.
When you're near the first building (#7), you can rest for a while. You won't be attacked by anyone for a while. Look around your surroundings and find the supply crates. When you're ready to go, head for the church (#8).
Open the door and enter the big hall (#9). Gather the ammo and use the regeneration points on the walls. Near the altar you'll find strange machinery (#10). Use the Gravity Gun to tear out the casing from I, and then throw something heavy in there. Prepare for a heavy fight.
First you'll be attacked by spiders. You'll hear a gunboat outside. Wait for the enemy soldiers to enter the church and kill them all. When the area is clear, go to the main entrance.
There's a small balcony to the left (#11). Here you can destroy the gunboat, using the rocket launcher (should you run out of rockets, there are some near the altar). When you shoot it down, go back to the church. Some new enemy soldiers will break in through the door (#12).
Turn right and enter the platform. There's a crate with rockets here (#13). Refill your ammo - you'll need it for another gunboat. The fight won't be easy. The chopper has a lot of free space to avoid the missiles, and you can only hide behind the sheets of metal that are easily destroyed by its attacks. When you destroy it, retreat back, as its pilot will decide to crush the airship into you.
Move to the edge of the platform and jump down to the planks (#14). Find a passage between the scaffolds (#15) go forth. You'll see an elevator (#16) that will take you right to the end of the scenario.