taken from Wikipedia
Chrono Trigger begins with the 1000 A.D. Millennial Fair, where Crono and Marle sample Lucca's
new teleportation device. Marle volunteers, but disappears through a strange portal when the machine
reacts with her pendant. Crono asks to be sent through the machine to find her, and discovers
he's traveled back 400 years. He meets Marle at Guardia Castle, and learns that a search party
looking for the missing queen of that era found her instead. Marle then vanishes; Lucca arrives
and claims that Marle's actually the princess of Guardia in 1000 A.D., and that since her ancestor
was not rescued, Marle ceased to exist. With the help of a talking amphibian called Frog, Crono
and Lucca rescue the real Queen, kidnapped by "Mystics" who worship the wizard Magus. Marle
reappears and the group returns to 1000 A.D., where Crono is placed on trial for allegedly
kidnapping Marle. He's sentenced to death, but breaks free from the prison. With Marle and
Lucca, he flees the king, to nearby Guardia Forest, where they stumble into a time gate.
They're shocked to find a devastated world filled with futuristic ruins, and uncover a video of the "Day of Lavos". The video shows a creature called Lavos erupting from the planet's surface in 1999 A.D and decimating the planet. The group resolves to prevent this catastrophe and recruit a robot named Robo before entering a new gate to arrive at the ethereal End of Time (year )—where an enigmatic old man offers advice, magical powers, and the use of several time gates. Crono and his friends hear that Magus created Lavos during the Middle Ages of 600 A.D., and that only a sword wielded by the "Hero" called the Masamune can defeat him. They find the sword's broken blade, deducing that the Hero is Frog and that the sword was somehow made by Melchior, who lives in 1000 A.D. Melchior notes that he needs Dreamstone, a rock found only in antiquity, to repair the Masamune. The group travel to 65,000,000 B.C. and meet the cavewoman Ayla, who gives Crono her Dreamstone after a friendly drinking contest. Ayla's boyfriend gets jealous of Crono, thinking that Ayla likes him better and steals the Time Key, but other than that they're able to get back without a problem.
Melchior repairs the sword, and Frog accompanies Crono as they set out to Magus's lair. They battle his three generals and confront the warlock in the process of casting a spell. Magus claims he did not create Lavos, who dwells within the planet to siphon its energy—but merely intended to summon it. The spell's interruption causes a massive time gate that swallows Magus's castle and everyone within. Crono and his friends awaken in 65,000,000 B.C.; after helping Ayla defeat the Reptites, they witness Lavos crash deep into the earth from above. Agreeing that Lavos is an extraterrestrial lifeform, the group travels to the ancient, enlightened Kingdom of Zeal in 12,000 B.C. Zeal recently discovered Lavos and seeks to drain its power to achieve immortality through the Mammon Machine. A mysterious prophet warns the kingdom's queen about Crono, forcing their return to prehistory with no way back, by sealing the time gate they used to get there. In 2,300 A.D. they find a ship-like time machine called the Wings of Time (or Epoch), which can access any time period without using a time gate.
For their final battle against Lavos, the team penetrate the creature's shell either through fierce fighting or by crashing the Epoch into it. They learn that Lavos has been harvesting DNA to control its own evolution. Lavos uses the amassed genetics to assume a final combative form, which the group vanquishes. At the final night of the fair, Crono and his friends say their goodbyes and adjourn to their own eras in time through the diminishing gates. If Magus joined the party, he departs to search for his missing sister, Schala. Crono's mother accidentally enters the time gate at the fair before it closes, prompting Crono, Marle and Lucca to set out in the Epoch to find her while fireworks light up the night sky. Alternatively, if the party used the Epoch to break Lavos's outer shell, Marle will help her father hang Nadia's bell at the festival and accidentally get carried away by several balloons. Crono jumps on to help her, but cannot bring them down to earth. Hanging on in each others arms, the pair travel through the cloudy, moonlit sky.
