Plot

It's been five years since everything was awesome and the citizens are facing the huge new threat of Lego Duplo, invaders from outer space, wrecking everything faster than they can rebuild.

Following the events of the first film, Finn's (Jadon Sand) (a young teenager in the real world, whose imagination drives the events happening in the LEGO universe) sister Bianca (Brooklynn Prince) (who is the reason why the aliens from the planet Duplo attacked Bricksburg) has been invited to share their father's LEGO collection; in the LEGO universe, this is represented by the arrival of Duplo aliens.

Emmet (Chris Pratt) (an every-man, construction worker and inexperienced Master Builder from Bricksburg) builds the aliens a heart as a token of friendship, but when one eats it and playfully demands more, Lucy (Elizabeth Banks) (Wyldstyle) interprets this as an attack and retaliates. The Duplo creatures cry and invade, making a mess of Bricksburg. President Business (Will Ferrell) (the former President of the Octan corporation and the LEGO World) unhelpfully tells everyone to "get along" before leaving to go golfing, but Emmet tells Lucy that "Everything can still be awesome."

Five years later, Bianca has taken some of Finn's LEGO creations and other toys in their basement to play with. In the LEGO universe, the Duplo army's invasions have turned Bricksburg into the post-apocalyptic underdeveloped wasteland Apocalypseburg, hardening its citizens. Emmet remains upbeat and wants to move into a dream home with Lucy but is troubled by visions of an impending cataclysm dubbed "Armamageddon".

A mini-doll named Sweet Mayhem (Stephanie Beatriz) (general Mayhem, law enforcer of the Systar System-Army) arrives and proclaims that Queen Watevra Wa'Nabi (Tiffany Haddish) (the shape-shifting alien queen of the Systar System) of the Systar System wants to marry Apocalypseburg's leader. Emmet watches as Mayhem's forces kidnaps Batman (Will Arnett), Lucy, Benny (Charlie Day) (spaceship-obsessed 1980's spaceman), MetalBeard (Nick Offerman) (a Master Builder who is a large bionic pirate with a severed head after he lost his original body in an earlier encounter with Lord Business' forces), and Unikitty (Alison Brie) to be sent to the Systar System. Batman eventually agrees to marry Wa'Nabi (when she makes insane promises to make them happy), while the others are placed in environments designed to tempt them, which only Lucy resists. Lucy believes that Wanabi's wedding to Batman will unleash the Armamageddon.

In pursuit, Emmet converts his dream house into a spaceship. He travels through "the Stairgate" - out of the basement - and is saved from an asteroid field by rugged adventurer Rex Dangervest (Chris Pratt) (a self-declared "galaxy-defender, archaeologist, cowboy and raptor trainer). Emmet begins to mimic Rex and hopes to impress Lucy with his tougher attitude. Lucy and her friends are taken to a spa; seeing her friends enjoying the catchy pop music, Lucy thinks they are being brainwashed and escapes to find Emmet. Rex and Emmet evade Wa'Nabi's forces and find Lucy. Emmet devises a rescue plan: Lucy will switch off the music, and Emmet will destroy the reception cake, encased in a temple, to stop the wedding.

As Lucy fights Mayhem, she learns that the Systar System never meant to antagonize Apocalypseburg, but merely failed to communicate their desire to coexist in peace - in the real world, Bianca simply wants Finn to play with her. She also discovers that Queen Watevra Wa'Nabi's original form was the heart Emmet gave the aliens. Realizing that Rex has sinister motives, Lucy tries to stop Emmet but manipulated by Rex, he destroys the temple.

In the real world, Emmet's destruction is carried out by Finn angrily destroying Bianca's LEGO creations. Emmet realizes his mistake but is seized by Rex, knocking Lucy onto a shelf. Now in the real world, she watches the siblings bicker. Aboard his ship, Rex reveals that he is an embittered version of Emmet from the future; abandoned for years underneath the dryer after crashing in the asteroid field, he became Rex - "Radical Emmet Xtreme" - and built a remote time machine to save Emmet. As revenge for being neglected while the other toys were played with, Rex has tricked his past self into bringing about Armamageddon (So that Rex himself never ends up underneath the dryer).

In the real world, Bianca and Finn's mother (Maya Rudolph) halts their bickering and asks them to put away their LEGO sets, representing Armamageddon (as in "Our Momma gets in"). Bianca puts Lucy in storage with the others, bringing an apparent end to the LEGO universe and Systar System that Lucy calls into question. In the real world, Finn hears Lucy and the others singing "Everything's Not Awesome" as Rex knocks Emmet under the dryer. Lucy rallies the others into escaping from the storage bin in various spacecraft and returning to the LEGO universe to save Emmet. Evading Rex's raptor Rexwing fighter squadron, Emmet and Lucy overpower Rex and destroy his time machine. Rex redeems himself as he and his time-line fade from existence.

Wa'Nabi and Batman finally wed, as Finn and Bianca agree to play together again. Their mother returns their LEGO sets and Finn repaired Bianca's creations, reversing Armamageddon. The LEGO universe is transformed into a mishmash of Apocalypsburg (reversing back to Bricksburg) and the Systar System: the peaceful "Syspocalypstar". Emmet's dream house is rebuilt, and Lucy reveals that she was one of the original artists of "Everything Is Awesome", much to Emmet's surprise.