This synopsis will contain spoilers!
An unknown woman buries a vellum containing the secrete to speaking to fire under a tree before her body is entirely consumed by fire from the inside out. Years later, Enna's brother Leifer discovers the document and learns its secrets. Enna returned to live with her brother after her mother became ill. When their mother died, she stayed to help with the house and with her brother.
Leifer begins to change with his new ability, becoming more easily inflamed, and when Enna confronts him after he disparages Isi (now married to Prince Geric), he burns her. Worried about him, Enna heads to the palace with Finn to speak with Isi. Isi, however, has her own troubles, as her ability to speak to the wind has become overwhelming, and she hears the voice of the wind constantly now. There is also war brewing in the south.
Enna goes with the army as they march south to meet the impending battle. Leifer reveals to the command his ability to speak to fire. During the battle, Leifer turns the tide, but is consumed by fire in the process. Enna, heartbroken, sees the vellum on him that contains the secret to fire speaking, and reads it. She learns the skill rapidly, but promises herself she will never use it on a person, tell anyone about her ability, or ever burn big like Leifer did.
Finn begins to grow distant from Enna and so becomes consumed with becoming a better soldier. When winter comes, the fighting stops and soldiers from Tira come to broker for peace. Nothing comes of it, however. When the Bayern decide to hold an auger to determine the outcome of the war, Finn volunteers. He is nearly killed, when Enna uses her power to burn the handle of the opposing warrior, and Finn emerges victorious. She decides she must use her skill to combat the Tiran invaders otherwise the auger will not be fulfilled.
She burns tents alone until Razo discovers what she is doing, and then they go together. Razo brings Finn for additional protection, and Enna learns Finn is in love with her while. They get greedy, however, and are nearly caught. Finn and Razo want to stop, but Enna won't, as she is obsessed with burning now. Isi tries to stop her, but she tries to burn Isi (now the Queen) and Isi deflects the attack with her wind. Enna goes off on her own, but it is a trap, and she is captured by a captain named Sileph.
Sileph is able to people speak, and he begins to manipulate Enna with lies and deception so she falls in love with him and burns Bayern outposts for Tira. Razo and Finn are captured trying to rescue her. Enna learns of Sileph's lies and is able to resist him at last. Finally, Sileph leaves for the final battle against Bayern, and Isi arrives in disguise to give Enna hope, though no offer of rescue. Enna escapes, rescues Finn and Razo, and they race to the final battle.
At the battle, Enna burns big and turns the tide of the war, but nearly consumes herself in the process. After weeks of resting, she is still not better, and Isi takes her to a people in the south who rumor claim worship fire. When they arrive they learn that they are able to speak with fire and live because they have also learned to speak with rain. Knowing two elements tempers the power of each. Upon realizing this, Enna and Isi realize they must teach each other what they know to save them both.
Their close friendship allows them to teach each other their skill, and they are immediately both saved. Isi, now nearly six months pregnant, hurries back with Enna and Finn so they can arrive before the baby is born. They return and the baby is born healthy. Enna and Finn are truly in love. Enna is admonished for her betrayal, but also rewarded for her bravery.
Shannon Hale the First Line of Enna Burning
Shannon Hale the Last Line of in Enna Burning