Story related, cannot be missed.
The following guide is taken from IGN's online guide for the game.
Into the Light starts off as the main tutorial in the tower. You cannot miss these quests since you have to complete them to complete the campaign. Note that this mission is logged as Out of the Darkness in your quest book once it is completed.
In lieu of any other missions being tracked, you will have these missions constantly monitored on your HUD. Help the first Fateweaver (Agarth) beat off the Tuatha and then travel east of Gorhart to locate the second Fateweaver to move the story onwards.
Since the second Fateweaver is rather out of the way, you may want to boost your character by completing the various side and (possibly) faction missions offered in Gorhart before you truly travel east to the Fateweaver. You will find the second Fateweaver slain, and the first guy will appear after you have some words with a mysterious woman.
Agarth will direct you to go Ettinmere after he buries the dead guy. This translates into taking your sweet time to complete side missions to gain experience and level up.Note that if you wander away from Ettinmere (east towards the Plains of Erathell), you may find Luminitsa the Fateweaver (near Didenhil) long before you meet Agarth once more. When you do, you will enter the dungeon known as Dellach and move the story forwards.
The dungeon itself is fairly straight-forward with Kobold enemies and Ettin brutes (and a Niskaru surprise). If you have Steel or Azurite equipment, you will find the dungeon ridiculously easy. Once you engage the Ettin War Priest and defeat him, enter the theater, kill the Tuathin gang-ambush, and you will unlock the last sub-menu option "Fate Twist" in your status. Speak to Alyn, the mystery elf lady who was at the dead guy's hut, then to Agarth. Once you do, you can head to Didenhil. The next mission is The Hunters Hunted.
The Hunters Hunted is offered upon speaking to Agarth after fetching the Fatestone from Dellach.
He will suggest you head to Didenhil in Glendara to start you off on kicking ass and taking names of the Tuatha. The front door is Hunter's Pit (West); the sneaky back door way is through Hunter's Pit (East). If you want experience points for monster killing, you may want the front door. If you like harvesting crappy components from traps, take the back door.
Head in and destroy the scrying glass the Tuatha are using. The surprise is the glowing dude who comes out (Gadflow). Confront him how you like, then speak to Agarth. Head to the Summer Court in Ysa after. Talk to Agarth to complete this quest and initiate Old Friends New Foes. As it is possible to Complete Old Friends New Foes anytime in the main quest line, you may have already completed it. if this is the case the Quest The Coming Storm will be initiated.
Old Friends New Foes is a next main quest when you wish to enter the city of Ysa. To initiate this, you need to speak with the Fae Sola at the entrance. Sola helpfully points you to Caer Nyralim in the southwest quad of The Sidhe.
Head there and locate Nyarlim before you proceed further east. Locate Nyralim (some big tree dude) and it will give you a task to whack a bunch of trolls and their mutant queen at the Haxhi Dam. Remember trolls are resistant against all elemental attacks. Unless you are an absolute god in combat, or have the game set to the easiest setting, you may want to increase your character's level to 14 to 16 before completing this quest.
The Tuatha red-shirts are tenacious but not tough; it's the trolls and boss troll you need to worry about. Slay them all and return to Nyralim to open the way on to Ysa. When you are ready, enter the dungeon. At this point, you will have either Sola or Alyn Shir at the entrance (neither really adds anything to the outcome) as an indestructible target ... or "traveling companion". While they sneak when you do, note that once you stand up in the presence of enemies, they immediately commit to assault. Defeat the troll boss.
Once you defeat the troll boss head back to Caer Nyralim and nab the objective to enter Ysa in The Sidhe. When you talk to Caer Nyralim there is an opportunity to persuade for help, complete that topic for a necklace accessory Nyralim's Grace. Once you gain entrance into Ysa, this quest is completed, and the Next Quest The Coming Storm Begins. You can only progress Further in that Quest However if you have completed all of the main story quests up to and including The Hunters Hunted.
The Coming Storm follows the split-up second quest (The Hunters Hunted and Old Friends New Foes). It begins as soon as you enter the City of Ysa.
With both quests completed, you can now visit the High King. In the Gardens of Ysa, head east into the Font, then into the Court of Summer. Place the Codex of Destiny and a scene occurs. Aftet the scene, you finally be awarded with a new Twist of Fate, and this achievement.