Sailor Moon's Adventures of Cars is the first episode of Season 5 in the Sailor Moon's Adventures Series, and the starting point of the Shadow Galactica Arc.
Kang the Conquerer arrives to begin the last few touches on the time machine that will revert all the madness occuring throughout the series back to normal. Meanwhile, as Chibiusa prepares to go back to the future, the soul of Chernabog frees Nehelenia and the Circus of Fear, who learn of Sailor Moon and Sailor Chibi Moon's survival as the Queen sends glass shards from her broken mirror to Earth. One of the broken shards falls in Mamoru's eye, while the disturbance interferes with Chibiusa's attempts to go back to the future. Meanwhile, Sailor Neptune and Sailor Uranus fight doppelgangers of the snow creature Marshmallow that appear from the glass shards. Sailor Pluto arrives with baby Hotaru, who gives Uranus, Neptune and Pluto the power to transform into their newly evolved and strengthened Super Sailor forms, just like the rest. After the battle, Hotaru suddenly starts growing up, and gives a warning of a revolution that will put the Moon Princess in danger.
The movie opens in the final race of the 2006 Piston Cup stock car racing season and championship in the Motor Speedway of the South, where a skilled but arrogant rookie racecar, Lightning McQueen, has overtaken his opponents, past a huge wreck, and has built up a huge lead over the cup's defending (but soon retiring) seven-time champion, Strip "The King" Weathers, and perennial runner-up Chick Hicks. However, because of his refusal to make regular pit stops and get new tires, his rear worn tires burst into flames on the final lap, causing him to skid and ultimately crawl to the finish line, barely managing to tie the King and Chick Hicks in a photo finish. Race officials announce that because the three racers are also tied in overall season points they will compete in one final tiebreaker race to be held at the Los Angeles International Speedway in one week to determine the champion. While traveling down Interstate 40 to California, McQueen becomes separated from Mack, his transport truck, and while trying to catch up becomes lost on U.S. Route 66, catching the attention of the local Radiator Springs Sheriff in the process. A chase ensues, during which McQueen crashes and gets tangled in wires, damaging part of the town's main street in the process.
Mamoru begins to act strangely, and Usagi becomes worried. Hotaru continues to grow up, and a visit from the spirit of Sailor Saturn awakens her to her past experiences. The spirit of Sailor Saturn inside young Hotaru awakens, and along with the Outer Senshi, she tries to warn Super Sailor Moon of the danger she's in. Super Sailor Moon becomes Eternal Sailor Moon for the first time with the aid of the nine Super Sailor Soldiers' combined abilities.
McQueen is taken to traffic court, where the town's attorney, Sally Carrera, pleads against McQueen. He is sentenced to repave the road using "Bessie", an asphalt-laying machine. Only interested in leaving and extremely furious, he makes an escape attempt before being hooked up, only to figure out his gas tank was siphoned. McQueen rushes through his first day of paving and the new road surface is so bumpy, unusable, uneven, and poor that he is told he must scrape it off and start over again.
People all around Tokyo, including Mamoru, become entranced by mirrors. Usagi remembers a shadow she saw in Mamoru's mirror, and races off with the other soldiers to find him. Just as she identifies that the shadow was Nehelenia, the dark queen drags Mamoru into her mirror world.
When Doc Hudson offers McQueen a deal -- beat Doc in a race around Willy's Butte and he is free to go -- McQueen eagerly accepts. He leaves Doc in the dust at the starting line, but loses control on the loose dirt turn and crashes into a cactus patch. While the town's tow truck, Mater, hauls McQueen out of the cactus patch in which he landed, Doc effortlessly cruises to the finish line after informing McQueen that he races like he fixes roads. McQueen is compelled to scrape off the botched pavement and start over again.
Mamoru gets taken through a mirror, and causes a time paradox; if Mamoru doesn't escape from Nehelenia's curse, Chibiusa's existence will disappear. Usagi transforms and follows Mamoru against her friends' wishes. The other Senshi teleport to Nehelenia's world to find Sailor Moon, but end up getting separated. Sailor Mercury and Sailor Uranus form a team and attempt to defeat Nehelenia, but their opponent, revealed as a clone, traps them in mirrors. Not long afterwards, Sailor Mars and Sailor Neptune also get caught in a trap.
As the ensuing days pass, McQueen is disturbed by nightmares of Chick Hicks winning the Piston Cup and landing Dinoco. He starts to befriend the town's residents and learn more about the town in the process: how Radiator Springs was once a thriving town until completion of the nearby interstate bypassed the little town, depriving it of its business traffic and visitors (and ironically, depriving those passing visitors of the natural beauty found in the scenery along the old highway); how Sally left behind her rich but unhappy life as an urban lawyer; what "tractor tipping" (a parody of cow tipping) is; and how Doc Hudson was once a famous racecar himself (the "Hudson Hornet") -- and 3-time Piston Cup champion -- until a horrible crash in 1954 ended his racing career.
Doc bitterly refuses to reveal much about his past (despite McQueen witnessing him expertly drifting through the loose dirt of Willy's Butte where McQueen crashed), labeling his old trophies as "a bunch of empty cups".
Sailor Mars and Sailor Neptune battle against another clone of Nehelenia, but after an exhaustive battle, they faint and get captured by Nehelenia. Meanwhile, Sailor Pluto and Sailor Venus also fall into captivity, while Sailor Jupiter sacrifices herself to save Sailor Moon, who fell under Nehelenia's hypnosis. One of Jupiter's rose earrings remains behind, and as Usagi looks at it, she remembers Tuxedo Mask. The hypnosis is broken, and Usagi makes her way through the final barrier to Nehelenia's castle, which is a stairway covered in thorns.
By the time McQueen finishes repaving Radiator Springs's main road, he has formed a bond with the town and its residents. Rather than immediately leaving for California (as he had initially been eager to do), he spends the day touring the town's businesses, receiving a fresh coat of paint and new tires in the process, and participates in a cruise party that night. But he is suddenly found, then whisked away in his truck, Mack, without even a chance to bid farewell to Radiator Springs. The town's residents are sad to see him leave, and Sally is angry to learn that it was Doc who ultimately informed the media of McQueen's whereabouts.
The final race among McQueen, The King, and Chick opens with what the race's commentators call the "biggest race in history." McQueen is distracted by his memories of Radiator Springs, losing time to The King and Chick Hicks, and begins to fear he will simply lose. To his surprise, Doc Hudson has arrived at the race, with Mater and a few others from Radiator Springs who will serve as his pit crew; Doc, once again wearing his original "Hudson Hornet" racing stripes, takes over as McQueen's crew chief. With Doc's coaching, a record-fast pit stop for new tires, and a few tricks learned from the small town's inhabitants, McQueen is not only able to overtake his opponents, but has built a considerable lead by the final lap.
As McQueen approaches the finish line, Chick sideswipes The King in a desperate attempt to avoid finishing behind him yet again, sending The King into a terrible rollover crash. McQueen, fearing that The King's racing career will end in the same way as did the Hudson Hornet's, comes to a full stop right before the finish line. After Chick gleefully crosses the finish line, McQueen then backtracks to push the veteran racer across the finish line ahead of him, saying that "I think The King should finish his last race". Although Chick Hicks has officially won the Piston Cup, he begins to learn that it's a hollow victory as he is jeered and despised for taking out The King, while McQueen is cheered as a hero for his good sportsmanship. Tex from Dinoco, The King's sponsor company, offers to support McQueen as his new sponsor; but McQueen, having now had a change of heart, respectfully declines, saying that his current sponsor Rust-eze gave him his "big break," and he wanted to continue with them.
Sailor Chibi Moon and Sailor Saturn face Nehelenia. Sailor Saturn attempts to use her Silence Glaive Surprise and unleash its deadly destructive powers, but Chibiusa stops her. Usagi finally arrives in time to see Chibiusa disappear as the curse progresses. When the nine Sailor Soldiers' energy and power helps Usagi transform into Eternal Sailor Moon, Nehelenia reveals that she experienced a lonely childhood, but that the mirror kept her company. Usagi's pity breaks the curse over Mamoru. Chibiusa returns, all of the other Sailor Soldiers are freed, and Eternal Sailor Moon's power returns Nehelenia to her childhood.
Two days after the race, McQueen returns to Radiator Springs, announcing that he will establish his racing headquarters there. This helps to revitalize the town and draw back visitors and tourists, with the once-abandoned Route 66 being reclassified as "Historic Route 66."