"Next thing we knew we were over South America courtesy of an agency we couldn't officially name, working for a guy who sent units like ours to early graves every day. Technically, our luck was improving."
The squad starts out in a river, and follows the path into a small village, where numerous buildings are burning and several militia soldiers lie dead. Searching through a large building, Sweetwater and Redford discover a trail that leads to Aguire, but before the squad can follow it, they are attacked by a force of Militia, supported by a PBL and a soldier armed with an M2 Carl Gustav. Taking heavy fire, Marlowe finds his own M2 Carl Gustav and engages the PBL, destroying it. After finding an old wooden boat for transport, Preston drives the squad down the river, with militiamen shadowing the boat along the way as a thunderstorm breaks overhead. After the boat runs aground in shallow water, the squad disembarks, but the militia launches an ambush from the jungle ahead of them. The team pushes through into a small hamlet, and rendezvous with a weapon crate dropped by Flynn to provide heavy firepower. The team then engages more militiamen, and acquire a PBL and head towards a logging camp, where the militia has dug in with heavy support, including an M939 truck and a KORD heavy machine gun, yet the squad pushes through into a small village. Engaged on both sides by militia units, the squad defeats the threat and advances forwards into another jungle, still following the trail of Aguire.
After running aground and being ambushed, head forward and go up the hill either side of the big tree instead of bearing right. The M-COM station is at the top inside a small wooden hut. Sarge will give an audio cue to destroy it.
Just before reaching Flynn's weapon cache, on the main route.
The level's title likely refers to the same-named novella by Joseph Conrad, Heart of Darkness. The main part of the novella takes place on a riverboat going up what is suspected to be the Congo river (the author never directly refers to the river's name, but does give strong evidence to support this theory), in search of an Ivory trader, who is discovered to have become mad and established himself as a god-like figure among the natives. The film Apocalypse Now is based in-part on the novella.
There is an MG3 placed by the wooden boat next to a house. This provides some extra firepower for the player as he/she wouldn't have unlocked many weapons so far in the campaign.
In the opening cutscene Preston says that they were now "working for a guy who sent units like ours to early graves. Technically our luck was improving." This may explain what happened to the squad after the events of Battlefield: Bad Company, and instead of being used as cannon fodder being sent on suicide missions like taking over Russian-occupied towns.
During the riverboat scene, Redford seems to have the 4x scope on his XM8 mounted on top of his grenade launcher's leaf sight. This also applies to the Red Dot on Haggard's XM8.
In the lumberyard area that one approaches on the patrol boat, once the enemy has been flushed out, if one were to stand around long enough in the piles of lumber, the other members of the team will begin to crack inappropriate jokes using the word "wood".
The PBL's gun is very effective against the troops in the lumber yard, as it is capable of firing rapidly and causes a lot of damage.
At the end of the level player can find the radio in the Militia outpost. The song played by radio is Boom by Colombian musician MC Magico.