Alanna and her twin brother Thom are ticked off because their dad is sending them away for training: Thom to become a knight (despite the fact that he wants to be a sorcerer) while Alanna's supposed to study magic and become a proper lady (even though she's a tomboy and hates magic).
Gee, does this seem a little backwards?
Thom seems resigned to their fate, but Alanna gets an idea: they look alike anyway (red hair, violet eyes, small frames) so why not switch places?
The twins tell their plan to Maude, the village healer, who's trained them in magic and looked after them since their mother's death. She's not too into it, but decides to use her magical Gift to ask the gods for help anyway.
While Maude is divining over a fire, she puts her hands and the twins' hands into the flame.
Even though it's Maude's spell, Alanna also has a vision: of a foreboding black city. But she keeps it to herself.
Looks like the gods are on the twins' side, because Maude's visions convince her to help the twins carry out their plan.
Thom forges his father's handwriting and writes a letter saying that he's to be sent to the City of Gods for sorcery training, while "Alan" is going to the capital for knight training.
Maude cuts Alanna's hair boy-short, and tells her that one of the things from her vision involved Alanna's Gift: she has the power to heal, and she must use it whenever she can in order to make up for all the deaths she'll cause as a warrior. Cheery!
Alanna rides off on her pony, Chubby, with her hood drawn over her head. Maude takes Thom down one fork of the road, while Alanna goes with Coram, a guardsman in her father's employ.
Coram thinks Alanna is Thom until a few hours on the road have passed, and when he finds out, he's Not Happy.
Well, on the other hand, Coram's always liked Alanna: she's quickly learned all the hunting stuff he taught her, while Thom's such a goofy weakling that he'll probably embarrass Coram at court. Not that Coram approves of this switching places business, of course.
In the end, Alanna talks Coram into going along with it—er, well, she actually threatens him into it, since she knows that he hates magic, and she can conjure apparitions that'll make him think he's going mad.
It helps that while on the trail, Alanna demonstrates her courage by calming Coram's huge horse when a snake frightens it. Coram knows that Thom would've been useless in that situation.
When they reach Corus (the capital city), Coram warns Alanna to watch her belongings. A lean young guy winks at Alanna and vanishes into the crowd.
The capital city is huuuge, and eventually they reach the palace, which is also huuuge. Coram leads them to the stables, where their belongings and horses are taken care of.
Coram warns Alanna to treat her noble sponsor with respect. Eek—what if he discovers her secret? But it's still way better than wife school.