To start the quest, you need to talk to Captain Lawgof. He can be found north-west of the Fishing Guild, near the coal trucks. You can utilise the lodestone network to travel to Ardougne, and then walk north-west to Lawgof.
Captain Lawgof welcomes you and asks if you want to become an honorary member of the Black Guard, apparently the finest dwarven regiment which can only be joined by the best of the best. When you accept, he explains that he lost contact with the south watchtower, making his base oblivious to any enemy advances. Just soon after this happened, goblins attacked and overpowered his men, demolishing the defences in the process.
Lawgof wants you to repair them so that the base remains strong. Agree to help him, and he will give you six replacement railings to use.
The damaged railings around the complex are bent; repair these by inspecting the appropriate sections of railing.
Just look to the bottom of the fence railings. The six bars that need fixing will not be straight lines, making them stand out.
If you fail to repair a rail, you may take 10 or 20 life points or your strength or crafting may be temporarily reduced. Whether you fail or succeed is plain random.
Fix the six broken railings and return to Captain Lawgof. He now wants you to send a message to the watchtower, to the dwarf-in-charge Gilob, saying that reinforcements will be sent as soon as the remaining goblins are defeated. Make sure you complete the conversation with Lawgof.
Head south to a ladder on a wide mound, surrounded by several wooden beams; this is the watchtower. Go up two ladders to the top and you'll find some dwarf remains in the corner. Pick them up and head back to Lawgof and speak to him. The remains will not appear if you did not finish talking to Lawgof.
Lollk's location.
Lawgof identifies the remains of Gilob, and tells you that he had a son, Lollk. He is missing, and Lawgof deducts that he must have been taken by the goblins to their hideout.
As the goblins keep coming from the south-east, Lawgof suggests you start there. Walk south-east, or use the Ardougne lodestone home teleport, to reach a cave entrance east of the Fishing Guild.
Once inside the cave, it will fork into three passages. Take the north-west passage to the furthest room from the entrance as shown in the map to the left. Look in the north-east corner, searching the northern-most box against the wall, until you find Lollk. Talk to him and he will thank you and run off to safety.
Return to Lawgof, who says that some goblins managed to slip past into the base and sabotaged the cannon. As he does not have any proficient men, he asks you to repair it for him.
Use the toolkit that he hands you, on the nearby cannon. You will need to match up three tools with the three mechanism parts to make it work. These must be done in order:
Use the hooked tool on the spring.
Use the pliers on the safety switch at the bottom.
Use the tooth tool on the gear located at the bottom of the hammer.
Nulodion's location
Back to Lawgof, he gives you yet another order. Now he wants you to get directions and ammunition for use of the cannon. The Weapons Development Chief of the Black Guard, Nulodion, is the dwarf you need to speak to. You must complete the entire conversation or you will not be able to open the door and talk to Nulodion.
Go to the Dwarven Mines outpost, north-east of Falador, and talk to Nulodion in the western building. Nulodion will give you an ammo mould and some instructions.
Finally, go back to Captain Lawgof and hand over the manual and mould to him. If you are interrupted during the conversation, he will take the mould but you will not finish the quest. You'll have to obtain another mould from Nulodion if this happens.