On a visit to one of Atlantis's important trading partners - a planet with a medieval-era culture - Sheppard and McKay meet a 13-year-old princess, Harmony, who must make a traditional pilgrimage alone to the ruins of the Temple of Laros before she can be crowned as her people's new queen.
Because Harmony is so young, one of her sisters begs the visitors from Atlantis to serve as secret bodyguards for the girl on her dangerous journey. For the sake of preserving diplomatic ties, Sheppard and McKay reluctantly accept the job.
Their route through the forested wilderness is stalked by a mysterious Beast that menaces all enemies of the crown, and Harmony herself is demanding, self-centered, and too smart for her own good. Unsurprisingly, she and McKay are soon ready to kill each other.
Then three Genii soldiers ambush them. They're after Harmony. Sheppard shoots them, but dozens more Genii are combing the woods. Because the details of the pilgrimage are supposed to be a state secret, someone in the royal family must have betrayed Harmony's location to the Genii - for unknown reasons.
Sheppard and McKay decide to return to town, but Harmony gives them the slip and plunges deeper into the woods, determined to complete her quest. Sheppard and McKay must follow her. They catch up with her and spend the night in a cave she has found. There, Harmony confidently proposes marriage to Sheppard, who is saved from answering when the Beast kills two Genii soldiers nearby, causing a distraction.
The next morning, the trio reaches the Temple, which turns out to be a mass of Ancient ruins. After Sheppard stuns two Genii guarding the site, McKay discovers that this is where the Ancients designed their drone weapons. The Beast is actually a cluster of drones that patrols the forest and kills those who do not carry the Ancient gene. Like McKay and Sheppard, Harmony has the gene. She also carries a pendant that she believes will glow if her gods favor her. McKay theorizes that the pendant is an Ancient access key that will give its holder control over the drones.
Unfortunately, the Genii have tampered with the Ancient machinery among the ruins. It's broken, and Harmony's pendant won't work. She is devastated, believing that her gods don't want her to be queen. McKay and Sheppard are dismayed, too, because the Genii forces are closing in. If the teenaged princess and her two protectors can't gain control over the drones, they will soon be captured or killed.