The Eternal Night covers Arcadia in shadow, leading to a long-awaited showdown between Gunmar and the newly transformed Trollhunter.
It's the end of the school year, and it's time for the Battle of the Bands, but at a very bad time. The Eternal Night has finally begun and the entire town will know the truth. Now that the time for war has come, the Trollhunters and their allies must unite and save the universe.
The ground under the bridge in the canals begins to crack open, conveying the approach of the Eternal Night when the radio host announces another one of Morgana's tremors, and School letting out for the summer. Meanwhile, Aja and Krel, and Douxie, and everyone else are preparing for the Battle of the Bands.
At Jim's house, Blinky is formulating their plan of attack with Merlin saying their focus should be Trollmarket and Morgana, not Arcadia and Gunmar. Just then, a third tremor hits, meaning the Eternal Night is in the hour. Jim declares Gunmar and Angor Rot his fight, saying that clearing the square first would be best to prevent any casualties. Strickler and Nomura agree to go with Claire and Toby to the Battle of the Bands to clear out the square while AAARRRGGHH!!! goes with Merlin to fight Morgana. Once their plan is set in motion, Jim confronts Merlin about the Darklands, worrying about the safety of the changeling familiars. Thankfully, he presents Jim with an evacuation plan for them all: a Cradlestone, which NotEnrique will be using to transport the babies out of the Darklands safely (with the assistance of Chompsky). With their task set, they jump through the fetch to evacuate the Nursery before it's too late. Barbara says goodbye to Jim and departs for the hospital, promising to be safe.
In the Forge, Gunmar recites his declaration for taking back the surface to his army while Angor Rot watches from the balcony. Morgana joins her champion. She briefly questions his faith, but he vows to kill Jim himself for taking his eye and his life previously. She vows that he will be ruling by her side when the world becomes hers. When he asks about Gunmar, Morgana replies that he's nothing more than a pawn for her master plan, and she will dispose of him when she gets what she wants. Angor, however, doubts if she actually viewed him as an exception.
Back at Jim's house, Claire and Toby dress into their newly crafted armors and gear up for their final battle.
In the Darklands, NotEnrique has second thoughts about this mission when he feels the tremors. Chompsky lifts his spirits with a moving speech (which is really just the English equivalent of jibber jabber).
At the Battle of the Bands, Aja and Krel finish their DJ debut, and Darci and Mary prepare to go on. Wearing her armor, Claire goes on stage and tries to announce the evacuation, but the girls just start playing thinking it's a new song. Finally, Gunmar tells Morgana all is ready, and she shoots a magic beam out of the Heartstone through the Staff of Avalon. The beam shoots out of the concrete ground of the canal into the sky, with Claire seeing it from the stage. Everyone begins to get a closer look at the beam, and begin evacuating when they see the Gumm-Gumms climbing out of the hole. As the eclipse draws closer and the day becomes darker, Jim prepares himself for his epic final battle with an assassin, a sorceress, and a warlord. Summoning the Eclipse Blade and climbing to the roof of his house, he recites these seven words: "At their darkest hour, I burn brightest". When the eclipse becomes total, he rushes headfirst to the battle jumping from rooftop to rooftop. In the canals, Gunmar's army is pouring out of Trollmarket, with Merlin and AAARRRGGHH!!! sneaking in with a Horngazel. AAARRRGGHH!!! sadly watches the Heartstone dying, with Merlin claiming that the death of Trollmarket along with it is a tragedy for tomorrow. The fight is now.
With sirens wailing and Gumm-Gumms surrounding, Claire, Toby, and the (former) changelings prepare for the fight of their lives with Claire wondering what could be taking Jim so long. Toby vows not to stop taking them down when the entire army appears. As a flying truck heads straight for them, Jim appears and cleaves it in half with his sword. The army is ready to give everything they have. But fortunately, so is the army Blinky has formed from their friends and allies from across the lands. The Trollhunters chop down the evil troll soldiers, saving Arcadia one rock at a time. With the city overrun, Jim tells Blinky and the others to get all the survivors to the school.
Meanwhile, Merlin and AAARRRGGHH!!! get inside the Heartstone to confront Morgana, only to be met by an attack by Angor Rot. AAARRRGGHH!!! holds his ground just fine against him until being blindsided by Morgana. Merlin tries to fight Morgana, but is easily defeated when he learns she drained the Staff of Avalon dry. As she handles him, Morgana sends Angor Rot after Jim.
The fight against the Gumm-Gumm Army is going according to plan as well, with Barbara at the hospital and Steve and Eli doing their "Creepslayerz" routine (with the exception of the boys becoming mesmerized by Nomura's intoxicating beauty). All of a sudden, Darci is dragged above the clouds by a Stalkling. Toby, using his gravity-defying Warhammer, charges on after her. Smashing it to pieces, he grabs his girlfriend, and they float back down like Mary Poppins, officially deciding to begin dating again. All of a sudden, a Nyalagroth bursts out of the ground. Claire and Toby prepare to fight when the Quagawumps appear, with the queens large cousin.
However, while the fight on the surface is stable, Morgana is mopping the floor with Merlin and prepares to deal a killing blow.
In Arcadia, things are still stable on Jim's side. Just then, the Gumm-Gumms all line up single file, announcing the presence and the approach of Gunmar and Angor Rot. As the one-eyed Gumm-Gumm warlord and the one-eyed troll assassin charge at Jim together from both sides, Blinky watches in awe and worry as Jim's final battle begins.
- Kelsey Grammer as Blinky
- Emile Hirsch as Jim Lake Jr.
- Charlie Saxton as Toby Domzalski
- Lexi Medrano as Claire Nuñez
- Jonathan Hyde as Stricklander
- Fred Tatasciore as AAARRRGGHH!!!/Señor Uhl
- Ike Amadi as Angor Rot/Detective Scott
- Rodrigo Blaas as Gnome Chompsky
- David Bradley as Merlin
- Clancy Brown as Gunmar
- Guillermo Del Toro as Dr. Muelas
- Grey Griffin as Queen Wumpa/Glug
- Lena Headey as Morgana
- Amy Landecker as Barbara Lake
- Diego Luna as Krel
- Tatiana Maslany as Aja
- Laraine Newman as Miss Janeth/Nana
- Colin O'Donoghue as Douxie
- Cole Sand as Eli Pepperjack
- Yara Shahidi as Darci Scott
- Lauren Tom as Nomura/Mary Wang
- Thomas F. Wilson as Coach Lawrence
- Bebe Wood as Shannon
- Jimmie Wood as NotEnrique
- Steven Yeun as Steve Palchuk
- Everyone in Arcadia finds out about the world of trolls.
- This is the second two-part episode, after the series premiere.
- It is discovered that Gunmar will die one way or another. If Jim doesn't kill him, Morgana will.
- When Chompsky and NotEnrique go into the Darklands to save the babies, one can hear the theme of Back to the Future.
- Getting Crap Past the Radar: Morgana's interaction with Angor Rot has some disturbingly sexual undertones, like how she strokes his face to reassure him that he's not a tool to her (which he quickly understands is a lie). It seems that, besides all the horrible things she put him through before, she still did much worse.