Heroes' Quest

Start
Talk to Achietties outside the Heroes Guild about joining the guild. Achietties will tell you to get three items: a Fire feather from an Entrana Firebird, a cooked Lava eel, and a Master Thieves' Armband.

Firebird's Feather
 Items needed: Combat armour, food, pickaxe.
 * In order to pick up the Fire Feather, you'll need ice gloves. Bring armour, a good weapon, a pickaxe, and possibly runes to kill the level 111 Ice Queen. Also, it is suggested to bring runes to teleport after you have the gloves, as it's a long walk back out.
 * Go to White Wolf Mountain (east of Catherby, west of Taverley). Enter the mountain at the south entrance, and walk/run north until you come to a rock slide. Use a pickaxe on the rock slide and go through it (this requires 50 mining). Once you are through, you will be near level 57 ice warriors and three ladders.
 * Use the South ladder, and go down the southwest tunnel. Go up the ladder just after the tunnel bends north. Once you go up, you will see level 53 ice giants there. There should be 2 ladders next to the one you came up. Take the East ladder down. Go north through the long tunnel with level 61 ice spiders and ice giants (the spiders in the tunnel do not show up on mini-map). The tunnel makes a loop, and ends at a ladder. Go up the ladder, then go down the other. Continue down the tunnel until it opens up into a large room full of Ice Warriors and the Ice Queen. Be careful, because this is a multi-combat area, so you will be attacked by multiple enemies at once!
 * If you stand behind the throne, you can avoid the Ice Warriors and can still attack the Ice Queen if positioned right. Kill her and she will drop the ice gloves. Once you have the gloves, exit using the  same route back, or teleport out if you brought runes. It's time to head to Entrana.
 * Make sure to bank your weapons and armour. Talk to the Monk of Entrana at Port Sarim to get to Entrana. Head to the northeast part of the island to find the Entrana Fire Bird. Kill it and it will drop the fire feather. Make sure you are wearing the Ice Gloves before picking it up.

Cooked Lava Eel
Items needed: Fishing rod, fishing bait, Harralander, vial of water, knife or slashing weapon (if traveling to Lava Maze).
 * Go to Port Sarim and talk to Gerrant at the Fishing Shop. He will give you a bottle of Blamish snail slime. Once you have the items, make sure you have fishing bait in your inventory while doing this, use the Harralander with the vial of water, then the unfinished potion with the blamish snail slime. Right-click the blamish oil and use it on a normal fishing rod to get an oily fishing rod.
 * There are two different locations where you can catch Lava Eel: the Taverley Dungeon or the Wilderness Lava Maze. It takes somewhat longer to reach the lava eel fishing spot in Taverley Dungeon (granted you don't have 70 Agility) but it's safer than travelling to Levels 40-45 in the Wilderness to reach the Lava Maze.
 * If you're going to the Lava Maze, make your way to the Wilderness border, preferably near Edgeville. Bring your oily fishing rod, some fishing bait, a knife or slashing weapon, and some food and a teleport to increase your chances of survival should anyone attack you; these areas of the Wilderness are usually desolate, but you never know. Wear nothing so that anyone you run across will have little interest in killing you. Also, take care not to go too far east near the Lava Maze, as there are deadly green dragons and potentially even player-killers there. Make your way to the western area of the maze where there are trees and spider webs. Navigate the maze and travel past some aggressive Black Knights to the southern/middle section where the fishing area is. Once you have some Lava eels, exit the maze and travel back to at least Level 20/30 Wilderness and teleport away. You can use the Wilderness Obelisk to the west of the Maze and the obelisk north-east of the Level 10-15 Wilderness mining site to be even faster, but the obelisk teleports are random, some obelisks are surrounded/near high-level monsters, and occasionally, people prey on people that use them, so this is quite a risk. Again, if you are killed, you will likely lose any quest items you are carrying and will also have to gather the items to make another oily fishing rod.
 * If you're going to the Taverley Dungeon, make sure you have the oily fishing rod and some fishing bait, and a dusty key if you already have one. You may wish to bring an Anti-dragon shield, armour, a weapon and food. Make your way to the Taverley Dungeon slightly southwest of Taverley and climb down the ladder. If you have 70 Agility (which is boostable) enter the pipe (be sure to wear your anti-dragon shield) and simply run south-east to the fishing spot and catch a few Lava eels. If you don't have 70 Agility, walk north and then to the east, you will pass level 18 and 22 Skeletons, level 19 Ghosts, level 13 chaos druids, level 31 Black Knights, level 42 magic axes, and level 20 Poison Scorpions. If you have the Dusty Key already, go over the bridge crossing the lava and north past the chaos dwarves and the lesser demons. Once you get past them, you must "Use" the Dusty key on the door to the west. You will then be in a room with baby blue dragons and blue dragons. If you do have 70 agility, simply go through the agility shortcut and head south until you see baby blue dragons.
 * If you don't have the Dusty Key, go past the bridge and continue southwest past hill giants and you will enter a fortress with a few Black Knights. Go to the east into a jail, kill the Jailer and then pick up his key. Use it with the jail cell holding Velrak the explorer. Talk to him to get the Dusty key. Head back north past the hill giants and over the bridge.
 * Go across the room, and down the tunnel until you get to three fishing spots (which are red whirlpool shapes, not the normal bubbly surface). This is where you can fish for the Lava eel. There are three Baby Blue Dragons which are aggressive if you are low-levelled, so be careful. Catch a few lava eels in case you burn any and then teleport/walk back out.
 * Once you have your eels, find a range or make a fire and successfully cook a Lava Eel to get a cooked Lava Eel.

Master Thieves Armband
For this part of the quest you will need the help of a player of the opposite gang. It is recommended to check the Oldschool Runescape forums or to visit the official clan chat, "OSRS SoA", which is dedicated for finding another partner during quests like this one.

Key:    Black Arm Gang (Italics)      Phoenix Gang (Bold)

For Black Arm Gang:
 * Go to Varrock and talk to Katrine, and she will tell you the gang password: "Four leafed clover.” (If you don't have black full helm and black platelegs you can buy them from the Champions Guild near Katrine, the black platebody can be obtained from Horvik's armour shop from Varrock as well.) She will tell you that you have to steal ScarFace Pete's Candlesticks who is in Brimhaven. You need to get the ID paper first though.

For Phoenix Gang:
 * Go to Brimhaven and find the gang office, which is the building east of the bar. Talk to Trobert and he will give you the ID paper, which you will need to get into ScarFace Pete's mansion. Before going to Scarface Pete's Mansion, you need to get a Black full helmet, Black platebody and Black Platelegs. Once you have the disguise, put it on. When you try to enter ScarFace Pete's Mansion you will be stopped by Garv. Show him the ID paper and he will let you inside. Go talk to Grip inside and ask him if there is anything you can do, and he will give you a miscellaneous key. Leave the building and give the key to your Phoenix Gang friend.
 * Wait until your Phoenix Gang friend is in their area.
 * Speak to Straven at the hideout to get the password for Alfonse. Get a bow and arrows before heading to Brimhaven. Note that brutal arrows will not work as they can not be fired                   through the hole in the wall. First, get the miscellaneous key from your Black Arm Gang Friend.

Now you and your friend should be at the same point.
 * Go to the Shrimp and Parrot Bar (not the southern bar) on Brimhaven. Once you are there, talk to Alfonse the Waiter and then to Charlie the Cook. Give them the password. Charlie the Cook will tell you about secret wall that you are able to push. The push-able wall is in the kitchen, same place as where Charlie is, near where you will see some Guard Dogs.
 * Once your friend is in place, go into the northeast room of the entrance and search the cupboard; Grip will then come into the room. Your Phoenix Gang friend will range him, and Grip will drop keys. 


 * Get past these and into the mansion by the west side door. Once inside, use the Miscellaneous Key on the north door. This brings you in a closet with a window into a room with a cupboard. Wield the bow and arrows, and shoot through the hole in the wall at Grip. He will drop the keys for your Black Arm Gang friend.
 * Using the keys, go to the treasure room, and take the Candlesticks. Give one Candlestick to your Phoenix Gang friend. Go out the way you came, and meet your Phoenix Gang friend. Go back to Varrock and talk to Katrine. She will give you the Master Thieves' Armband.


 * Your Black Arm Gang friend will get two Candlesticks and trade you one of them. Go back to Varrock and talk to Straven to get the Master Thieves' Armband.

Ending

 * Go back to the Heroes' Guild, talk to Achietties outside and give her the three collected items.

Rewards

 * Access to the Heroes' Guild
 * Ability to wield Dragon battleaxe and Dragon mace.
 * 3,075 Attack experience
 * 3,075  Defence experience
 * 3,075 Strength experience
 * 3,075 Hitpoints experience
 * 2,075 Ranged experience
 * 2,725 Fishing experience
 * 2,825 Cooking experience
 * 1,575 Woodcutting experience
 * 1,575 Firemaking experience
 * 2,257 Smithing experience
 * 2,575 Mining experience
 * 1,325 Herblore experience
 * 1 quest point
 * Access to the Fountain of Heroes

Trivia

 * If you have completed the quest and are a part of the Black Arm Gang, you have the ability to help others who have not completed the quest and are members of the Phoenix Gang. First, you can enter the mansion without your full black armour and ask Grip for another miscellaneous key for your partner. Open the cabinet and allow Grip to walk into the room. Shut the door and trap him and the Phoenix Gang member must kill Grip. This will update their quest journal for Heroes' Quest.
 * Members of the Phoenix Gang who have already completed the quest also have the ability to help others who have not, and are members of the Black Arm Gang. Either use the Miscellaneous Key received while completing the quest initially, or get a new one from the Black Arm Gang member. Return through the Shrimp and Parrot bar to the kitchen, and then through the secret panel. Head past the guard dogs again and into mansion. Use the Miscellaneous Key on the door, and kill Grip once the Black Arm Gang member has lured him into position.