Will Treaty, a young Ranger in the kingdom of Araluen, wants to free his friend Alyss from a traitorous nobleman named Keren, who is keeping her imprisoned in Castle Macindaw. Macindaw is a fortress in Norgate Fief, a section of land protecting the northern border of Araluen from invasions by the Scotti warriors in the neighboring kingdom of Picta.
Keren wants to rule Norgate Fief. In order to gain power, he has poisoned his uncle, Lord Syron, who now lies near death in Castle Norgate. Keren also poisoned Syron’s son Orman, but he is recovering in Grimsdell Wood with the local healer Malcolm.
Will is the only authority figure who can oppose Keren and lay siege to Castle Macindaw. He finds some shipwrecked Skandian warriors who owe him a favor. Their leader, Gundar, agrees to fight with Will against Keren.
In Macindaw’s tower, Alyss waits patiently for Will to contact her. Keren has interrogated her numerous times. Since he uses a blue gemstone to hypnotize her, she always answers his questions truthfully. Alyss is a clever Courier, a diplomat who serves the king, so she keeps a lantern in her cell to send coded messages to Will in Grimsdell Wood. She also keeps a small vial of acid to slowly corrode the bars of her cell, day by day.
Will shoots a hollow arrow through Alyss’ window, an arrow containing a note and a small black pebble. Malcolm the healer says that if Alyss concentrates on the pebble instead of on Keren’s blue gemstone, she’ll be able to resist his influence the next time he tries to hypnotize her.
Will also hears that an unknown knight has been seen in the area, and when he goes to the local inn to investigate, he’s delighted to discover that the knight is his childhood friend Horace. Horace is a skilled knight sent by Crowley, the commander of the Rangers, and Halt, Will’s mentor, to aid Will in bringing down Keren. Horace understands siege techniques well, but doesn’t think that a fighting force consisting of himself, Will and 25 Skandian raiders will be enough to overthrow Keren’s men in Macindaw.
Keren comes to Alyss’ cell to question her, but by holding the black pebble and focusing her mind on Will’s image, she avoids being hypnotized. Keren thinks she’s in a trance when she hears that the Scotti general MacHaddish will arrive at Macindaw within a few days. Keren plans to allow the Scotti to invade Araluen so that he can get money and buy a title for himself.
Although Keren wants to back out of his plans for betraying his country to the Scotti, his poison finally kills Lord Syron. Now that he has actually murdered a relative, he doesn’t feel that the king of Araluen will forgive him. Alyss uses her signal lantern to tell Will about MacHaddish’s visit.
MacHaddish and a small group of warriors visit Macindaw to consult with Keren, and when they leave, Will attacks them. After a skirmish with the Scotti warriors, Will tracks a wounded MacHaddish through the woods and nearly loses in hand-to-hand combat with him. Horace arrives to help Will, and the two lead MacHaddish and a few other injured Scotti to the Healer’s Clearing, Malcom’s camp in the woods.
In order to get information from MacHaddish, Will asks Malcolm to arrange an unusual interrogation. Malcolm is a master of deception as well as a great healer, and he dresses up as the legendary sorcerer Malkallam in order to scare MacHaddish. Malcolm tells MacHaddish that a Scotti demon is loose in the woods.
Meanwhile, his assistants hide in the woods, using sound and light projections to display a demon’s head and other frightening illusions. Malcolm says that he will allow the demon to attack MacHaddish unless MacHaddish reveals all the battle plans that he made with Keren.
MacHaddish says that the Scotti, led by a man named MacFrewin, will come through the mountain pass from Picta in three weeks. They will occupy Castle Macindaw and use it as a base of operation. They intend to occupy all of Norgate Fief and then attempt to expand their reach throughout Araluen.
This information spurs Will into action. He knows he must occupy Castle Macindaw before MacFrewin arrives, or else the Scotti’s invasion will succeed. Will develops a plan for Malcom to distract Keren’s men with a scary illusion on one side of Castle Macindaw while the Skandians use ladders to scale the other side and sneak in.
Keren stops interrogating Alyss when he visits her cell. Instead, he begins chatting with her and discussing his problems. He brings up the fact that if the Scotti occupy Macindaw, she’ll be a prisoner for years. He offers his hand in marriage as an alternative to the slave’s life she would face with the Scotti. She turns him down, saying that she could never marry without love and could never love a traitor.
Will and Horace decide to attack Castle Macindaw at night. As the soldiers on the ramparts of Macindaw rush to watch Malcolm’s illusions in the forest, Will, Horace and the Skandians scale the opposite castle wall and start fighting. As the Skandians rout Keren’s men, Keren himself runs to Alyss’ tower. Will pursues him up the stairs, fighting off several soldiers in the process.
When Will arrives in Alyss’ cell, Keren has hypnotized her with his blue stone again. Keren orders Alyss to kill Will. Alyss is about to carry out the order, but Will confesses that he loves her, which snaps her out of the trance. Alyss throws her vial of acid in Keren’s face, and he stumbles and falls out of the tower’s window. Keren’s few surviving soldiers surrender, and the siege of Castle Macindaw is successful.
In the aftermath of the battle, Alyss spends some time recovering from the shock of nearly killing Will. Will frets that Alyss doesn’t remember that he confessed his love for her, or worse, that she does remember and won’t mention the incident because she doesn’t return his feelings. Alyss vaguely recalls Will saying he loved her, but she’s afraid it was only a dream caused by her own wishful thinking.
Orman regains his health and takes his place as lord of Macindaw again. Reinforcements arrive from Castle Norgate to help make sure that the Scotti don’t try to attack. With his assignment neatly wrapped up, Will prepares to return to Seacliff Fief, his original posting.
Orman sincerely thanks Will, Horace and Alyss for their services to Norgate Fief, and the three friends travel south. They reach a fork in the path, and Alyss travels to Castle Redmont, Horace to Castle Araluen and Will to the Gathering Ground to meet his Ranger mentors and report about the siege of Macindaw.
Will and Alyss both feel uncomfortable as they part ways, each of them having romantic feelings for the other and each thinking their feelings aren’t returned. When Will finishes meeting his mentors and returns to Seacliff Fief, he feels a deep sense of loneliness. His spirits rise when he receives a letter from Alyss that says that she hopes he loves her because she loves him as well. Overwhelmed with happiness, Will rushes to pack a bag and saddle his horse for a journey to Castle Redmont.