In a bold heist, the infamous Moriarty, disguised as a clever pie mascot, seizes control of London's Natural History Museum, taking the city's tiny gnomes hostage. The authorities, spearheaded by the brilliant detective Sherlock Gnomes and his steadfast companion Dr. Watson, initiate a quick rescue operation to apprehend the villain. After an exciting showdown, Moriarty appears to meet his end, crushed beneath the mighty weight of a dinosaur skeleton.
In parallel, star-crossed lovers Juliet and Gnomeo, now blissfully united, set out from their charming Stratford-upon-Avon garden towards the vibrancy of London. They stumble upon a quaint yet neglected new garden, where they are quickly thrust into leadership roles by the esteemed duo of Lady Bluebury and Lord Redbrick. However, their seemingly perfect relationship begins to unravel as Juliet becomes increasingly obsessed with revitalizing the garden, unintentionally sidelining Gnomeo. In an effort to rekindle her attention, Gnomeo embarks on a quest to find a rare Cupid's Arrow orchid, with directions from Benny via an old computer. The adventure takes an unexpected turn when a falling stall sets off the alarm at the flower shop, compelling Juliet to dash to Gnomeo's aid. Their confrontation reaches a peak with Juliet's stern words: > "The garden can't wait, and neither can I!"
As tension escalates, they receive a distress signal over Benny's walkie-talkie, alerting them to an unknown danger lurking in their garden. Rushing back, they discover their gnomes have vanished, and are soon joined by Sherlock Gnomes and Dr. Watson. The duo, counting on a mysterious clue card they've found, hesitantly allows Juliet and Gnomeo to join them in piecing together the garden's puzzling events.
Following the trail left by Moriarty, Sherlock embarks on a journey through Chinatown's twisting alleyways, leading him to Curly Fu's Emporium where another cryptic clue awaits. Evasive maneuvers are required as they narrowly escape the wrath of guards resembling angry felines. However, rather than dive into the museum's mysteries, Sherlock opts for a moment of artistic indulgence at a nearby gallery, insisting it aids his cognitive process. Gnomeo, seizing the chance for some insight, encourages him to refocus, only to be dismissed dismissively. Juliet, siding with Sherlock, leaves Gnomeo feels ignored and hurt.
In a moment of realization, Gnomeo comprehends his error in leaving Juliet's side but it's too late. While exploring the maze-like corridors of the museum, he falls prey to a menacing stone gargoyle, with Watson left stunned. As Sherlock becomes increasingly caught up in his own ruminations, he decodes the next clue that leads him and Juliet to disguise themselves in squirrel costumes for infiltration of a canine's territory on a lawnmower. Their initial triumph quickly turns to dread as Gnomeo confronts an existential threat poised by the imminent fireworks display.
The urgency intensifies as Juliet and Sherlock discover another tantalizing lead that brings them to a doll shop, where they meet Irene, Sherlock's bitter ex-fiancée. Though she initially repels them, she ultimately grants Juliet access, revealing pivotal information that sends them toward Traitor's Gate at the Tower of London. Here, a shocking truth unfolds: Watson, previously perceived as the mastermind behind the chaos, admits to just pretending to be Moriarty in an attempt to forge a deeper connection with Sherlock. Yet, this ploy takes a surprising turn as the gnomes simply vanish.
The true puppeteers of this predicament are revealed to be the gargoyles, who whisk away Juliet, Sherlock, and Watson onto a ship bound for uncharted waters, leaving the trio to contemplate their next strategic move against the odds.
As the investigation reaches its climax, Sherlock uncovers a monumental discovery: the captured gnomes are imprisoned beneath the iconic Tower Bridge, submerged in a pool of sweet pie filling. Just as he’s on the verge of solving the case, Professor Moriarty emerges from the shadows, disclosing his masterful orchestration of Watson's unwitting assistance in his wicked scheming. Moriarty aims to crush the gnomes using the very framework of the city itself—the colossal bridge, which is now teetering on collapse.
The villain's nefarious plot deepens as he engineers a false alliance between the gargoyles and Watson, allowing him to snoop on the doctor’s map and effectively locate every gnome across London. Meanwhile, Sherlock’s turbulent relationship with Watson spirals to a breaking point as he observes his partner's ill-treatment at Moriarty's hands.
Determined not to be hindered by their recent estrangement, the renowned detective duo agrees to unite for one final, daring mission to save the gnomes. They board an unmanned drone, racing toward Tower Bridge as the countdown clock ticks ominously.
In a breathtaking display of ingenuity and resolve, Gnomeo executes a brave move, getting the Red Goon Gnomes to perform a captivating dance, providing a much-needed delay in the impending disaster. This interval allows him to reunite with his beloved Juliet, and together, they thwart the sinister gargoyles' plans.
Simultaneously, Dr. Watson leaps into action, liberating the trapped gnomes from their sugary confinement with nothing but a modest bar of soap. Nevertheless, Moriarty's villainous plot continues, as he launches a vicious strike on Sherlock, leaving the detective wounded and grappling for defense.
In a desperate act of valor to rescue his comrades and foil Moriarty's machinations, Sherlock makes a dramatic sacrifice, lunging at the villain just as the bridge is set to plummet. Watson, ever the devoted friend, seizes the moment to deploy his trusty cane grappling hook, rescuing Sherlock from imminent peril and sending Moriarty cascading into the depths below.
As calm returns, the gnomes emerge triumphant, their freedom safeguarded amidst a dazzling fireworks spectacle. In the forthcoming spring, Gnomeo and Juliet unveil their meticulously crafted garden, welcoming Irene and the feline guardians to partake in the festivities. With Sherlock and Watson's partnership rekindled, they bid adieu to each other, embarking on yet another enthralling adventure, bound together by an unbreakable bond of loyalty and trust.
