Plot

A war-weary former army captain is inexplicably transported to Mars and reluctantly becomes embroiled in a conflict of epic proportions.

John Carter, a Civil War veteran, who in 1868 was trying to live a normal life, is "asked" by the Army to join, but he refuses, so he is locked up. He escapes and is pursued. Eventually they run into some Indians, and there's a gunfight. Carter seeks refuge in a cave. While there, he encounters someone who is holding some kind of medallion. When Carter touches it, he finds himself in a place where he can leap incredible heights, among other things. He later encounters beings he has never seen before. He meets a woman who helps him to discover that he is on Mars, and he learns that some kind of unrest is going on.—rcs0411@yahoo.com

Civil War vet John Carter is transplanted to Mars, where he discovers a lush, wildly-diverse planet whose main inhabitants are 12-foot-tall green barbarians. Finding himself a prisoner of these creatures, he escapes, only to encounter Dejah Thoris, Princess of Helium, who is in desperate need of a savior.—IMDb Editors

Barsoom, the red Martian cities of Helium and Zodanga have been at war for a thousand years. Sab Than (Dominic West), Jeddak of Zodanga, armed with a special weapon obtained from the Thern leader Matai Shang (Mark Strong), who tells Sab Than that he serves the Goddess who has chosen San Than to receive the special weapon & is blessed to rule Barsoom with none to oppose him.

Sab Than uses the weapon to lay waste to most of Helium. He proposes a cease-fire to the Helium King and an end to the war by marrying the Princess of Helium, Dejah Thoris (Lynn Collins). Dejah is also a scientist & has developed a weapon of her own, using the elusive 9th ray of the sun, to fashion an energy source of unlimited power. She demonstrates it to the king, but a Thern spy sabotages the weapon. Dejah knows that Sab Than has simply discovered the weapon first. She hates Sab Than intensely.

After the sudden death of John Carter (Taylor Kitsch), a former American Civil War Confederate Army captain, his nephew Edgar Rice Burroughs (Daryl Sabara) attends the funeral. As per Carter's instructions, the body is put in a tomb that can be unlocked only from the inside. His attorney hands over Carter's personal journal for Burroughs to read, in the hope of finding clues explaining Carter's cause of death.

The anecdote recounts back to the Arizona Territory, where Union Colonel Powell (Bryan Cranston) arrests Confederate captain Carter. Powell, knowing about Carter's military background, seeks his help in fighting the Apache. However, Carter escapes with the marshals in pursuit.

In an ensuing chase, both Carter and Powell find themselves in a cave in which Carter had been searching for gold. A Thern appears in the cave at that moment; Carter kills him and, with the help of his medallion, is unknowingly transported to ancient Barsoom (Mars). Because of his different bone density and the planet's low gravity, Carter is able to jump high and perform feats of incredible strength. He is captured by the Green Martian Tharks and their Jeddak emperor Tars Tarkas (Willem Dafoe).

The Princess Dejah Thoris escapes in one of Heliums ships & is flying over Tharks territory, when attacked by the pursuing forces of Sab Than. DEjah is rescued by Carter, who sees that Dejah is a human. He then jumps all over the place & attacks SAb Than's ships pursuing Dejah. Sab Than wants to use the weapon to eliminate Carter but is persuaded to take Carter alive by Shang. The Tharks (who are sick of being in the crossfire of the fight between Helium & Zodanga) are mighty impressed by Carter's feat. Dejah proposes a union between Tharks & Helium to defeat Zodanga, but is rebuffed by Tars Tarkas, who wants to use Carter for his own purposes & to gain mastery over whole of Barsoom.

Dejah understands that Carter is from Earth & hence has a different bone density which enables him to perform his feats. They are caught in the forbidden Thark temple, which means the death punishment for Sola as she was deputed to guard Dejah & Carter. Tars reveals to Carter that Sola is his daughter & implores him to run away with her & Dejah & to sail down the sacred river Isus to find the answers he seeks. Tars also gives Carter the medallion which was found on his person when he first landed on Barsoom.

Carter, Dejah, and Tarkas' daughter Sola (Samantha Morton), embark on a quest to get to the end of a sacred river to find a way for Carter to get back home. They reach the end of the river Isus & find a strange structure that activates as it comes in touch with the medallion. Dejah realizes that the ninth ray can be activated by a series of code words, which acts as instructions to transport people even across worlds. She obtains more information about the ninth ray, a means of utilizing infinite energy and also the key to understanding how the medallion works. But they are later attacked by Shang and his minions, the Green Men of Warhoon. The Thern were tracking Carter's progress & as he got near to the Thern secrets, Shang decided to step in & take control of the situation.

Carter valiantly fights the Warhoon army all by himself, when a Helium ship arrives to save Dejah. Turns out it was Dejah's father guided by SAb Than. They take Dejah & Carter back to Helium, while Sola manages to escape. The demoralized Dejah grudgingly agrees to marry Sab Than, then gives Carter his medallion and tells him to go back to Earth. She also gives Carter the phrase that would activate the medallion to transport him back to Earth.

While Dejah thinks Carter has left, Carter decides to stay to save Helium from Sab Than and is captured by Shang, who explains to him the purpose of Therns and how they manipulate the civilizations of different planets. Shang says that he plans to eliminate Dejah after her wedding to Sab Than, so that no one with knowledge of the power of 9th ray is left alive. Carter is able to make an escape as he and Sola go back to the Tharks requesting their help. There they discover Tarkas has been overthrown by Tal Hajus (Thomas Haden Church). Tarkas, Carter, and Sola are put on trial in a Colosseum battle with two enormous vicious creatures. After defeating them and killing Hajus, Carter becomes the leader of the Tharks.

The Thark army charges on Helium and defeats the Zodangan army by killing Sab Than. Shang just manages to escape. Carter becomes prince of Helium by marrying Dejah. On their first night, Carter decides to stay forever on Mars and throws away his medallion. Seizing this opportunity, Shang banishes him back to Earth. Carter then embarks in a long quest, looking for clues of the Therns' presence on Earth and hoping to find one of their medallions; after several years he appears to die suddenly and asks for unusual funeral arrangements-consistent with his having found a medallion, since his return to Mars would leave his Earth body in a coma-like state. He makes Burroughs his protector, giving him clues about how to open the tomb.

The story reverts to the present, where Burroughs runs back to Carter's tomb and opens it only to find it empty. Shang, in the form of a butler, suddenly appears, having followed Burroughs. But as he prepares to kill Burroughs, Carter appears and kills Shang. He then tells Burroughs that he never found a medallion; instead, he devised a scheme to lure Shang out of hiding. Carter takes his medallion, whispers the code, and is then transported back to Barsoom.