Okay, here goe's.
The green riders wear green uniforms and they serve the king of sacoridia. There is some magic in the way they are chosen or rather called into service. They come to the castle of the king driven by a calling they cannot explain and find themselves presented with a box of brooches, winged horses, take one and suddenly hear the sound of hooves, an unexplicable longing, an urge to do something. Thus they become green riders and each one develops a certain talent like telepathy, weather-forecast or healing.
Karigan ist not a green rider. She is a seventeen-years old merchant's daugther, stubborn as a mule, and has just run away from school after some trouble with a noble boy she had unfortunately defeated in a sword's play. She just wants to get as far away from the school as possible. That she happens to stumble over a dying green rider who trust her to bring his last message to the king and is henceforth persecuted by a sinister grey figure and a couple of very roughhanded villains who would like nothing better than to get the message and kill her first, seriously disturbs her own plans. She obeys all the same, not knowing why she does it, mounts the dead riders horse - who turns out to be a faithful companion - and succeeds in bringing the message to the king through several strange, mysterious, dangerous and even humorous adventures. At the king's castle the adventure takes an unexpected turn. The magic, elven-like people of Eletia whose mere existence is doubted seem to be mixed up with it somehow, also politics start to get difficult and so does love. Above all Karigan realizes that everybody judges her a green rider with a calling now and that's about the last thing she wants to be. She really tries hard to leave the castle and the other riders and in the end just manages to save the king and whole sacoridia and yet get hurt in a a way that makes a sequel inevitable.
So it does in the second volume, "First Rider's Call". We learn that the continent Sacoridia belongs to was conquered by some people coming over the sea, resembling the spanish coming to america, who fought the natives for several decades in a terrible war. In this war the green riders were founded by their first famous (female) captain, who tries to reach out through the times now to Karigan. For the evil that came to Sacoridia then in the person of a young and power-hungry prince who was seeking immortality in one way or the other is not yet vanquished. Mornhavon the Black is somehow still alive and creeps back into existence much stealthier than Voldemort and much more sinister. It is one of the things I love most about Kristen Britain's books that life of her characters just goes on as usual and the magic and adventure just sips into it from all sides, slowly, almost unnoticed at first, then building up and threatening, sinking away again ...it's just convincing. In this second book the magic of the riders fail, their quarters are burned and their companionship is put to the test. In the end it is Karigan, now a fully fledged green rider almost against her will, who has to take on the greatest risk and face Mornhavon the Black alone. With the help of an ancient memory of a magician (he insists on being a memory, not a ghost or something, and he does have to feed the cat first before helping to defeat Evil) she manages to send Mornhavon into the future. But nobody knows how far into the future ...
So we had to be back for a third book. It is called "The High King's Tomb" and appeared last fall. This time Karigan is entrusted with the training of a youn man who is called to be a rider but turns out to be a case not unlike she herself was, when she first joined the crew. Karigan does not feel meant to be a teacher and when her charge gets them nearly drowned and the place the ferryman, who insists on calling her "Sir", brings them to turns out to be barely respectable lodging she KNOWS she's not meant to be a teacher. Yet that young man turns out to be the only one can save the lady Estora, the woman the king of Sacoridia, Zacharias, had to marry for political reasons when he really loves Karigan - and she tries hard and unsuccesfully not to love him in return. Still, Estora has to be saved for the sake of peace and Karigan reaches the king in time although she has to take a short cut through death's antechamber to do so. And then there's still Grandmother, that mysterious figure working for the destruction of Sacoridia with her black magic at hand and her string of wool causing pain and death and a fourth volume soon.
Kristen Britain works as a ranger in a national park and there's a lot of her personal experience in her books, especially she knows about horses. I specially like that sense for companionship among the green riders she displays and for me she's a genius in interweaving magic and everyday-live. I have never seen another fantasy book where people did need a restroom, where a captain of a magical crew had to do lists and papers (or had them done by her secretary) and the heroes compared their favourite chocolates to one another. I strongly recommend the books fro reading and re-reading.