Clodagh embarks on a quest to retrieve her brother from an evil fairy, in the process falling in love with a broody warrior named Cathal and helping him to discover the truth about his past and fight for freedom against his oppressive father. Clodagh is the daughter of the Chieftain of Sevenwaters Keep, who feels she is not ready to settle down into the normal life of a noblewoman, like her sister Deidre. During the days leading up to Deidre's wedding, Clodagh meets Aidan and Cathal, two of her Uncle's warrior men who have come to attend the wedding. Aidan is very good-looking and charming whereas Cathal is more churlish and rough around the edges. Despite being attracted to Aidan, Clodagh has no intentions of marrying anyone any time soon. At the moment, she's more worried about her mother, who is pregnant and may not survive the birth because she is quite old to be giving birth. There's also lots of tension building up between the different warring clans of people who live near Sevenwaters, which is Clodagh's forest home. There are rumors that Fey folk may also be causing trouble and increasing the friction between the "chiefdoms".
During the eve before the wedding ceremony, Clodagh and Aidan dance and Clodagh finds herself liking Aidan even more. Later that night, however, she receives a strange warning from Aidan's friend, Cathal. Cathal tells Clodagh that Aidan is not for her and that she should make sure to stay away from him. Clodagh is tired of men and trying to understand the way they think. The next few days, Clodagh continues to clash with the crusty Cathal and learns that Aidan is actually already betrothed and that's what he meant by asking her to stay away from Aidan. Clodagh is hurt and surprised that such big news was kept hidden from her and she spends the rest of the week avoiding both Aidan and Cathal. One day, Aidan finally catches Clodagh by herself and explains that his betrothal is only a formality between his father and the girl's father and that the girl he's betrothed to is only twelve years old and someone he doesn't even know. Aidan thinks that Cathal just told Clodagh this information because he's jealous and likes Clodagh, as well.
A few days later, Clodagh's mother gives birth to a baby boy named Finbar. One night, Clodagh receives a visit from Cathal who tells her he has to leave on a mission. To her surprise, he kisses her, leaving her more befuddled than before. As Clodagh sits by the fire thinking about the strangeness of the situation, she hears a noise from the crib where her baby brother is and realizes that it's time for his feeding. When she looks in the crib, however, all she sees is some moving bits of moss, sticks and stones, shaped to look like a baby. Clodagh realizes with horror that her brother has been replaced with a fairy changeling. To make matters worse, no one else sees the bundle of moss and sticks as a fairy baby.
Clodagh's father thinks that Cathal's late night visit is too coincidental and that he may be involved in the kidnapping of the baby. Clodagh tries to convince her father that the fey folk are involved but since he doesn't see the bundle of moss and sticks moving and crying. He thinks Clodagh is just imagining things because she's so upset. Aidan also reveals that Cathal didn't even tell him where he was going. This compounds everyone's suspicions that Cathal was involved. Clodagh's father sends out his men to search for Cathal. As the days pass, there are attacks on nearby holdings and everyone thinks Cathal is somehow involved in these as well. As the household is turned upside down due to the chaos after Cathal and Finbar's disappearance, Clodagh feels an increasing urgency to find out how to return the changeling to the fey folk.
She sneaks out one day to try to find a way to the Otherworld where the fey folk reside. On the way out, she is almost caught by Aidan who has been instructed to hunt for Cathal. She ends up running into Cathal who shelters her in a cave. He remains mysterious as to his motivations but, surprisingly, he is able to see the changeling baby as what it is – not just a bundle of sticks and stones. Against her better judgment, Clodagh agrees to get Cathal's help as the man claims to know how to enter the Otherworld. Just before they reach the magical river that will take them to the Otherworld, Aidan catches them. Aidan demands that they stop and is heartbroken to see that Clodagh seems to have run away with Cathal.
Clodagh and Cathal roam the Otherworld and Clodagh gets to know more about Cathal. Cathal remains inscrutable and refuses to talk about his past and his family though he has a magical cloak sewn with all sorts of charms that somehow keeps them warm and dry despite the rain and river water. Cathal reveals that he never wanted to visit Sevenwaters and that he knew that all the chaos and troubles that have befallen Sevenwaters is somehow due to him. As they travel the Otherworld, looking for a fey folk settlement, they are attacked by fey-crows, tricked by a fey-dog, almost be-spelled by a charmed field of flowers and finally have to battle a rock-creature which almost kills Cathal. Finally the two arrive at a settlement of some sort where they are greeted by the same dog-creature that Clodagh thought was trying to trick them. The dog-creature tells them to rest for a bit before he brings them to the Lord of the Oak.
One day, Cathal has a vision of someone that looks like him appearing in the forests of Sevenwaters and killing Aidan. Cathal is devastated that this vision might reflect something that is happening as they are trapped in the Otherworld. Cathal thinks someone has been impersonating him and doing evil deeds. When the dog-creature finally returns, he informs them that Mac Dara, the Lord of the Oak, is ready to see Clodagh. Clodagh doesn't want Cathal to come with her because she doesn't want to risk his life so she goes out alone. When she finally meets Mac Dara, she realizes that he is Cathal's birth father as he looks almost exactly like Cathal. She realizes that Mac Dara has been the one who has been wreaking havoc in Sevenwaters and making everyone believe Cathal was the culprit.
Mac Dara reveals that he orchestrated the whole kidnapping of Clodagh's baby brother just so that he could have leverage to get his son, Cathal, back. Even though Clodagh refuses to let Mac Dara have Cathal, the Lord of the Oak tricks Cathal into coming into his magical Hall where he uses his powers to trap him. Cathal tells Clodagh to take Finbar and go home but she promises she will come back for him.
After passing Finbar to her sister for safekeeping, Clodagh immediately returns to the Otherworld where she decides to strike a bargain with Mac Dara. She tells him that she only wants to see Cathal one more time so that she can conceive a child with him so that she will always remember him in some way when she returns home. Mac Dara is impressed by her bravery to come back to his realm and agrees to give her one night with Cathal. Apparently, many months have passed in the Otherworld even though only one human day has passed for Clodagh so Cathal has been trapped in the Otherworld for a while. During his lengthy imprisonment, he's been tricked by his father by visions and apparitions of women who look like Clodagh so it takes a while for Clodagh to convince him she is truly who she is. Once they reunite, they make their escape.
Just as Clodagh and Cathal reach the entry back to the human world, they are attacked by Mac Dara and somehow Clodagh finds herself in Mac Dara's grasp. Cathal saves Clodagh from his father by somehow using his magical powers over water which he inherited from his mother. Mac Dara ends up letting Clodagh and Cathal go without a fight and appears desolate as he watches the two leave his world.
The story ends with Clodagh and Cathal having to smooth things over with Clodagh's father and the chieftains of the other clans before they are allowed to be married.
Best part of story, including ending:
I like that this story is rich in Celtic mythology with regards to the Celtic people of the times and their relationship with the fey folk. I like that Juliet Marillier explains about the different kinds of fey folk - from the familiar tall, beautiful and elegant fairies to the other kinds of fey folk, like the "Old Ones" who blend in with the boulders and the natural landscape.
Best scene in story:
My favorite scene was when Clodagh returns the baby changeling to its fey parents. Mac Dara didn't care about the baby changeling and he had thrown it into the fire as a show of how cruel and heartless he can be. Clodagh rescues the baby changeling from the fire and tends to its wounds. It was a very touching scene when the fey parents got their baby back.
Opinion about the main character:
I like that even though Clodagh should be angry that the Fey Folk may have stolen her brother and replaced him with a changeling, she instead shows compassion and nurtures the baby changeling. This shows that she understands that it wasn't the baby changeling's fault for being used as a pawn in the scheme of things. I like that Clodagh wasn't petty and uncaring and found a "nobler" way of resolving her problems.