During a mission to Kerberos, one of Pluto's moons, an expedition team, consisting of Shiro, Matthew Holt, and Samuel Holt, is attacked and imprisoned by a hostile alien craft from the Galra Empire while Galaxy Garrison—Earth's primary institution for space exploration—has presumed them dead. One year later on Earth, Garrison cadets Lance, Pidge and Hunk witness a vessel crash land and learn it contains Shiro, who has been quarantined after escaping from the Galra. As they form a rescue plan, Keith—a talented, but reckless academy washout—arrives and rescues Shiro before the five of them escape into the desert. Shiro is unable to remember anything from his captivity, but the group is able to determine the Galra are searching for a weapon known as "Voltron". Using what they know, they find a large robotic blue lion hidden in the desert and learn that Voltron is a robot formed from the blue and four other robot lions. The Blue Lion accepts Lance as its pilot and takes the five through a wormhole to the Castle of Lions on Arus, where they find Princess Allura, her royal advisor Coran and four space mice in cryostasis. Upon awakening, Allura is shocked to discover that 10,000 years have passed since they were placed in cryostasis. Haggar, advisor of Zarkon, leader of the Galra Empire, senses Allura's return and Zarkon sends Galra troops commanded by Sendak after them. Allura names the others as Voltron Paladins, bestows them with armor and bayards (the Paladins' weapons) and tasks them with finding the other lions. Lance and Hunk retrieve the Yellow Lion while Shiro accompanies Pidge to find the Green Lion. The Red Lion, as it is unfortunately revealed, is in the hands of the very Galra ship advancing on Arus. Unsure of whether to run or fight, Allura consults the artificial intelligence formed by the memories of her father, King Alfor, who admits he was wrong to hide Voltron and encourages her to fight. Keith, Shiro and Pidge infiltrate the ship so Keith can find the Red Lion while Shiro and Pidge, who repurposes a Galra drone dubbed "Rover", search the ship for prisoners, revealing to Shiro his father and brother were the other missing astronauts from the Kerberos mission Shiro was on. With all four lions retrieved, the Black Lion is released from the Castle and selects Shiro as its Paladin. All five Paladins use their lions to fight the Galra, and succeed in uniting to form Voltron and destroying Sendak's ship before accepting their new roles as the Defenders of the Universe.