A Sea of Shields by Morgan Rice is the tenth book in The Sorcerer's Ring series. As the story opens, Gwen is giving birth to a baby boy who will later be named Guwayne. There are magical omens as the boy is born and later as he goes through the first formal ceremony. His parents can feel the tremendous power in his tiny body from their first encounters with him. However, the source or reason for this power is not revealed in this book. Gwen is taken home by Ralibar and wakes days later to discover that her mother is near death, offering final words of advice for Gwen, who is now queen of their kingdom. Meanwhile, Gwen is preparing for the double wedding in which she will marry Guwayne’s father, Thorgrin. Also to be wed are Gwen’s brother Reece with his betrothed, Selese. But, while Reece is in the Upper Island he encounters a childhood love, Stara. She is also his cousin. Their union is forbidden. However, while they are there, Reece pledges to stop his wedding and to return for Stara.

Stara’s father is Tirus, now in prison but formerly the king of the Upper Island. Tirus discovers the situation between Stara and Reece and he sends his son Falus to make sure Selese knows of the love between Stara and Reece. Falus presents Salese with some scrolls written between Stara and Reece when they were children and she doesn’t realize the scrolls are old. In despair, she goes to the Sorrows Lake where she wades in and drowns herself.

Meanwhile, Reece arrives home and visits his mother on her deathbed. His mother already knows of Reece’s plans to call off the wedding, and she makes him see that his actions affect everyone in the kingdom. Reece realizes she’s right and rushes to find Selese. When he finds her, she is already dead. Reece is devastated. He finds Falus and kills him aboard his own ship, prompting a revolt among the Upper Islanders. When Glen makes this discovery, she insists that Reece go to Tirus and apologize, hoping that will smooth things over between the warring MacGils and McClouds. Reece intends to do as she asks; but, his honor cries out that an apology is wrong. He kills Tirus instead.

While this is going on, Gwen’s sister, Luanda, is living in exile in the mountains. She hates her situation and blames Gwen for it though her beloved husband, Bronson, pledges his allegiance and obedience to Gwen. Luanda wants a baby in the worst possible way but fears it will never happen. She’s briefly allowed home but is heartbroken when she’s again sent away. Back in exile, she discovers she’s expecting a baby and rushes home to share the news with Bronson, only to discover that he has been murdered by the revolting McClouds. She blames Gwen who had recently released hundreds of captured McClouds in an effort to create a peace between the clans. Luanda knows that she holds the key to the shield that protects the entire kingdom from invasion. She goes to the shield and is preparing to break it open just as Romulus is trying to break in from the outside with his army of dragons.

As this attack is taking place, the McClouds have joined to attack the King’s Court, where Gwen is in residence with Guwayne. Thor is on a quest to find his mother and the Silver, the elite knights of the kingdom, are on an annual pilgrimage. Gwen’s brother Godfrey arrives just in time to warn Gwen’s people of the attack and to slam the gates of the city closed against the McClouds. As the story comes to an end, Gwen and her people are evacuating the city while Godfrey and a few soldiers are holding off the McClouds, the Silver trying to rush back to join the fight. Luanda is just about to break through the Shield, knowing that Romulus might very well kill her and Romulus is hoping that Luanda is the key to finally breaking in.