The book is set during the events of The Green Ember.
"A Green Ember story set during Heather and Picket's arrival at Cloud Mountain, The Last Archer follows the journey of Jo Shanks. Jo is a gifted archer with a burden on his back and a fire within. Eager to see the Longtreaders receive justice, he travels from his Halfwind Citadel home to a Cloud Mountain poised on the brink of war. What he finds there will confront his convictions and test his resolve as the war begins and King Jupiter's heir is revealed. A kingdom in the balance. An arrow aimed at the heart of darkness. Who will take the shot?
Jo Shanks is an archer of Halfwind Citadel, disliked by his superior officers and burdened by a great desire to better himself in archery so as to prove himself to the world. He prepares in earnest for the upcoming Archer's Cup. Meanwhile, he hears that there will be a Citadel Congress at Cloud Mountain--a meeting of the Lords and highest officers of each secret citadel. Word has it that Lord Rake has been harboring Longtreaders, dangerous relatives of the traitor Garten Longtreader.
With the help of his friend Lund and some hard work, Jo Shanks enters the Archer's Cup, only barely losing to Nate Flynn of the Bracers. After Flynn wins the Cup, he asks Jo to join his team of Bracers to accompany him to Cloud Mountain.
One night, he is assigned to a post upon the slopes of the Mountain, in a shelter situated high above the forest below. When he detects movement in the forest below him, he and the few rabbits with him, under the leadership of Captain Frye, come down to see what the matter is.
On the forest floor, they are attacked by wolves. As they attempt to escape from the great number of their foes in the darkness, Jo comes upon one of his fellow Bracers, who is about to be killed by one of their attackers. Joe attempts to rescue him by slaying the wolf with an arrow from his bow, but he misses. A wolf attacks and wounds Jo, causing him to go unconscious. He is carried to the infirmary deep within Cloud Mountain, where he awakes to find himself upon a sickbed.
During his stay at the infirmary, he meets the medic Emma, who wraps his arm in bandages so as to prevent infection. While upon his bed, his thoughts turn to the events of the previous night, in which he once again had failed to hit the mark when it mattered the most. Although Nate Flynn attempts to cheer him up, it does him no good, for he has disappointed himself and most probably everyone else.
Then suddenly, wolves attack the infirmary. Determined to prove himself this time, Jo takes up his bow and climbs out of bed to assist his fellow soldiers fighting the wolves within and without the Mountain. Eventually, he reaches Captain Frye and gives chase to a group of wolves within the forest.
He and the soldiers who are with him assist a trapped band of archers against the wolves, but they are soon all trapped and many of them slain by the wolves. Jo himself, who is wounded, finally gets up when all the wolves have left to see if he could get help. He doesn't go very, far, however, and soon he finds himself upon the forest floor, unconscious.
When he wakes, he sees a white rabbit speeding down the mountainside. When she sees him lying where he is, wounded, she stops suddenly to help him to sit up against a tree. She calls for help, and asks him his name. Jo recognizes her as one of the Longtreaders, who are said to be traitors. She leaves him there, and there he rests for a few hours, drifting into sleep.
When he awakes once more, the forest is still; but not long after, he sees the white rabbit again, running up towards Cloud Mountain citadel. Nearby, Jo spots a few wolves preparing to slay her before she can reach her destination. Without really thinking why, Jo grabs a bow and arrow, and shoots at them. This time, he does not miss his mark, and without stopping to see who had rescued her, the strange white rabbit continues treading up the mountain. Jo drops to the ground again and faints from sheer exhaustion.
He awakes in the infirmary once again, where Emma explains to him how the Longtreaders had rescued Jupiter's heir from death at Jupiter's Crossing. He realizes then that he had played a small part in that rescue by his saving Heather Longtreader from death in the forest, upon the slopes of Cloud Mountain.