The central plot of "Guardians of the Galaxy" revolves around the theft of a seemingly simple Orb by Peter Quill on the planet Morag. It is soon revealed that the Orb contains the Power Stone, one of the six immensely powerful Infinity Stones. The fanatical Kree warrior, Ronan the Accuser, seeks the stone on behalf of the cosmic tyrant Thanos. However, upon acquiring it, Ronan betrays Thanos, embeds the stone into his warhammer, and plans to use its power to single-handedly destroy Xandar, the capital of the Nova Empire, in retaliation for a peace treaty he despises.
The Guardians—Quill, Gamora (Thanos's estranged adopted daughter), Drax, Rocket, and Groot—unite, initially through circumstance in the Kyln prison, and later by choice to prevent Ronan from unleashing the stone's power. A major turning point is Groot's sacrifice; he forms a wooden shield around his friends as Ronan's ship crashes, uttering "We are Groot" to signify their unity before being destroyed. In the final confrontation on Xandar, Quill distracts Ronan with a bizarre "dance-off," allowing Drax and Rocket to destroy Ronan's hammer, freeing the stone. Quill grabs it, and his ability to survive its overwhelming power is the film's biggest reveal. The Guardians link hands, sharing the energy, and use it to obliterate Ronan.
The ending contains two key revelations. First, Quill gives a fake Orb to his mentor/captor Yondu, swapping it for a troll doll, and delivers the real Power Stone to the Nova Corps for safekeeping. Second, the Nova Corps reveal that Peter is only half-human; his father was a member of an ancient, unknown celestial species, which is why he was able to hold the Infinity Stone. This sets up the central mystery for the sequel. Finally, Quill opens the last present from his dying mother, a cassette labeled "Awesome Mix Vol. 2," symbolizing his acceptance of his past and readiness to move forward with his new family.