Normal boy Mateo realizes he's the defender of dreams against Nightmare King. He faces creatures from dreams crossing into reality, questioning what's real.
After sharing an incredible dream, Mateo and his sister, Izzie, realize the Dream World is real when Mateo's comic book hero, Z-Blob, comes alive and follows them back to Brooklyn. But when Mateo's ex-best friend, Cooper, is captured in the Dream World by evil nightmare creatures and can't wake up, Mateo and Izzie discover there are Waking World consequences to what happens in their dreams.
In defiance of the evil Night Hunter and his grimspawn, Mateo and Izzie free Cooper only to need a rescue of their own. Luuckily, their science teacher, Mr. Oz, is actually a secret agent of the Night Bureau. In the heat of battle, Mateo wakes up and brings a night terror back with him to Brooklyn, which he and his friends must defeat without their Dream World powers.
To craft their own hourglasses and become official dream chasers for the Night Bureau, Mateo and his friends must defeat a giant sand guardian and enter the Dream Forge before the Nightmare King's forces destroy it. But when there's a dreamer in need, the kids must choose. Will they face the forge and become more powerful dreamers, or will they help their friend?
As the clock runs out to face the Dream Forge, Mateo and his friends enlist the help of the mysterious Dream Bandit and her abilities to manipulate time. Mr. Oz and Albert defend the forge from a grimspawn onslaught while the dream chaser hopefuls enter the forge and face their deepest fears. But they must hurry: if the forge is destroyed before they finish, they may never become dream chasers!
The search for the Sandman leads Mateo and the others to the tallest mountain in the Dream World, Pillows Peak. Only the Sandman can repair Lunia's hourglass, which the Nightmare King will stop at nothing to control. When a friendly competition turns spiteful, the Nightmare King is alerted to the kids' location and orders an assault on the mountain.
A surprise visit from the Chief Inspector Strick of the Night Bureau forces Mateo to hide Z-Blob. When the lovable Dream World anomaly escapes to explore Brooklyn, Mateo must track him down before anyone sees him. Meanwhile, while the gang handles Strick, who was zapped by a device that makes a person live out their last dream, making Strick act like a toddler and cause havoc in the observatory.
Logan and Mateo are facing off over who will ask Zoey to be on their Sheep Week team, and Logan will do anything to win. When they have a face-off in the video game based Cyber Realm, Logan accepts a cheat code from a stranger, which corrupts the entire realm! With the help of the Cyber Realm Guardian, the kids must stop the virus or lose the realm to the Nightmare King forever.
Backs to the wall with a surprise math test and the opening round of the Sheep Week games, Mateo and his friends track down their math teacher, Ms. Putnam, in the Dream World to find the test's answer sheet. But it turns out that within sweet little Ms. Putnam is a ginormous inner rage just waiting to be let loose.
Desperate to prove his worth, Logan is blindsided when he delivers Lunia's hourglass to Lance, who is really the Nightmare King! Held hostage in the Shadowkeep, Logan makes a surprising new friend in the grimspawn Sneak, until they are forced to do battle. Meanwhile, Mateo and the others are in a battle of their own on the soccer pitch in the Sheep Week finals.
It's all hands-on deck to rescue Logan from the clutches of the Nightmare King, but Oz and the kids quickly learn that there are more dangerous creatures lurking in the Grim Realm than just grimspawn. In the Shadowkeep, Logan is sprung from his prison cell by his grimspawn ally, Sneak. But why would a grimspawn risk it all to save an agent of the Night Bureau?