Paradox Junction: Main Quest

The quest

The main quest of Paradox Junction follows the crew of eight as they befriend the Twins, two girls trapped in the town, and kill the Dark Heart that keeps Nuketown in its time loop. It needs the Blundergat and its upgrade, the Sundergat, though several steps can be done before them. Steps 3, 4 and 5 can be done at the same time, in any order.

Step 1: building the Blundergat and the Sundergat

The swing

In Past Nuketown, shoot the swing of the Yellow House Backyard and take the Swing Seat.
From round 8, in Nuked Nuketown, find the RC-XD controller: by the boxes to the right of the Pack-a-Punch, against the fence of the Green House garden, or on a shelf at the back of the Yellow House Garage.
Drive the car over a ramp into a backyard, up a second ramp, over a wall of debris and through a hole in the wall, then blow it up against the garage door.
Walk into the open garage, watch a corpse turn to ash, and take the Chalk.
Put the Swing Seat and the Chalk back on the swing chains of the Yellow House Backyard: the Twins appear.

Strange Tree, hopscotch and music box

In Nuked Nuketown, open the red toolbox of the Yellow House Garage for the Irradiated Seeds.
In the past, plant them in the mound of dirt to the left of the Pack-a-Punch on Trinity Ave., and fill the small tree with souls using the Blundergat or the Sundergat.
In the nuked era, throw a Combat Axe at the grown tree three times for three pieces of Strange Firewood.
In the past, lay the wood in the fireplace of the Yellow House and set it alight with a Molotov.
In the nuked era, stand on the large X of Trinity Ave., facing Der Wunderfizz, until it stays blue. In the past, the Twins draw a hopscotch there.
Hop from 1 to 12 and back to 1, avoiding the black smoke, without leaving the board. A golden music box appears: fill it with souls using the Sundergat and escort it to the fireplace of the Yellow House.

Hopscotch

The game drawn in chalk by the Twins, the way they open every door in the end.

Piano lesson and bouncing ball

In Nuked Nuketown, wait in the Green House Backyard for the Piano Teacher, a slow zombie that walks in from outside the map. Turn her with Brain Rot or a Psych Grenade and follow her to the piano of the Green House.
As soon as she sits at the piano, switch to the past: she plays and explodes.
Back in the nuked era, find eight glowing musical notes around the map. Each blinks from one to eight times; interact with them in that order.
In the past, play the notes on the piano of the Green House in the order shown on the wall, always 8-6-7-5-6-5-3-5.
In the nuked era, kill the three floating zombies outside the map behind one of the houses, then go to the new X on Trinity Ave.
In the past, the Twins draw a circle with a ball. Kill every zombie the ball throws into the air before it lands. Fill the golden sheet music with souls using the Sundergat and escort it to the piano.

Toy box and four square

With Wisp Tea and Death Perception, go to the Pack-a-Punch in Nuked Nuketown. Shoot the top of the pole of loudspeakers outside the map to the left, and let the Wisp bring the fallen Goggles in.
With Death Perception, find the Headset: by the trash cans next to the GobbleGum Machine of the Cul-de-Sac, on the coat rack of the Green House Upstairs bedroom, or in the hand of a headless mannequin in the Yellow House Backyard.
In the past, use the blue toy box near the chalk circle.
In the nuked era, shoot down the red ball, on munition crates of Trinity Ave., on the roof of the M8A1 house, or on the Yellow House mezzanine, and roll it with shots to the X behind the Green House.
In the past, the Twins draw a four square in the Green House Backyard. Bounce the ball from square to square with melee hits until the timer ends, then fill the golden cymbals with souls using the Sundergat and escort them to the toy box.

The clock and the Twins

With the music box, the sheet music and the cymbals in place, shoot the hands of the broken clock of Nuked Nuketown to 0.
Start the switch to the past and, during the switch, shoot the red hand once more.
A white orb appears over the Cul-de-Sac and moves to the piano, the toy box and the fireplace, turning into the Twins at each. Be there each time.
The Twins wait at the swing of the Yellow House Backyard with a yellow portal. Talk to them to start the boss fight.

The Dark Heart

The heart floats above the town, throwing slow meteors that mark their impact on the ground and fire tornadoes that burn and slow the players; a Molotov in their path turns them aside. It has three phases, each opened by clearing black goo from the piano, the music box and the fireplace, then defending a Concentration Field around each:

Phase 1: fill the Loot Cyst beside each pile of goo with souls. Its glowing orange spots take the most damage. At one third of its health, a Max Ammo and a Max Armor drop in front of the Green House.
Phase 2: Rad-Hounds join the zombies. Shoot the green orb above each pile and kill what comes out of it.
Phase 3: Shock Mimics join in. Lead a Tortured Zombie to each object and kill it there, then bring the heart down.

A chalk drawing of the Dark Heart hanging over two houses, between the two Nuketowns, Paradox Junction, Call of Duty Black Ops 7 Zombies

The Dark Heart in chalk

The Twins drew it hanging between the two Nuketowns.

Paper Hearts

A document of the map: “There’s a monster in the sky.”

The ending

The heart dies, and its soul passes into a piece of chalk. The Twins thank the crew, then draw a hopscotch that opens a portal to the Agarthan House, and warn that the next stop is somewhere cold. A team that keeps playing goes back to the Cul-de-Sac with every perk, Bonus Points, Aether Tools, Aetherium Crystals, Legendary weapons, Salvage and a random wonder weapon around it.

The Zombie Twin in front of a blue portal showing the Agarthan House, ending cutscene, Paradox Junction, Call of Duty Black Ops 7 Zombies

The portal

The Zombie Twin in front of the blue portal to the Agarthan House.

Rewards

The Standard Completion calling card of Paradox Junction, Paradox Junction, Call of Duty Black Ops 7 Zombies

Standard Mode

The Paradox Junction Standard Completion calling card, the Heartbreaker skin of the Blundergat and 10,000 XP.

Directed Mode

The Directed Completion calling card, the Timeshatter skin and 5000 XP.

Early completion

A calling card for the quest finished before Directed Mode came out, on April 2, 2026.

Cursed

The Void Storm, Ardor Storm and Sanguine Storm Pack-a-Punch camos on Tiers I, II and III, and the Dead End calling card on Tier III.

Round 100

Starting the boss fight at round 100 or later makes it harder, with fewer armor plates and only Armored Zombies in the last phase, and earns a Dark Ops calling card.